Entomology Lecture Notes PDF

ENTOMOLOGY MARITA S. LABE, Ph.D. Professor, Department of Crop Protection WHAT IS AN INSECT? - it is classified under Phylum Arthropoda characterized by 1. having jointed legs or appendages 2. segmented body that bears varying number of paired and segmented...

ENTOMOLOGY MARITA S. LABE, Ph.D. Professor, Department of Crop Protection WHAT IS AN INSECT? - it is classified under Phylum Arthropoda characterized by 1. having jointed legs or appendages 2. segmented body that bears varying number of paired and segmented appendages 3. bilateral symmetry 4. sclerotized exoskeleton that contains the nitrogenous polysaccharide, chitin 5. various internal features such as open circulatory system, Malpighian tubules (generally) and in most, a system of ventilatory tubules, tracheoles and tracheae having 2 subphyla a. Chelicerata. (Characterized by a pair of appendages near oral opening) spiders, mites, ticks, scorpions, horseshoe crabs b. Mandibulata. (Characterized by a pair of grinding structures associated with mouthparts) insects, centipedes, millipedes - it is ranked under Class Insecta CLASS INSECTA - has several distinct traits 1. three well-defined body regions or tagmata, i.e. head, thorax and abdomen 2. three pairs of legs in adult stage 3. commonly one or two pairs of wings, if any 4. single pair of segmented antenna on the head 5. a pair each of maxillae and mandibles 6. 2 kinds of eyes (compound and simple) 7. Relatives of Insects (under Phylum Arthropoda) Class Arachnida (spiders, mites, ticks, scorpions, etc.)  Little evidence of external segmentation  Tagmata: prosoma (cephalothorax) and opithosoma  Prosoma: chelicerae, pedipalps and 4 pairs of legs; simple eyes present; no antennae Entomology | 53 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)   Opisthosoma: without locomotor appendages  Gonopore: hidden in anterior part of ventral surface of opisthosoma (embryologically segment 2) Class Crustacea (crayfish or crawfish)  Tagmata: varied; head and thorax covered dorsallyby an unsegmented carapace (shieldlike plate) and distinctly segmented abdomen  Appendages: biramous (composed of 2 branches)  Compound eyes on long stalk  Head appendages: 2 pairs of antennae (feelers), 1 pair of mandibles and 2 pairs of maxillae  Gonopores (external opening of reproductive tract): 1 pair located on the base of posterior appendages of thorax Class Chilopoda or Symphyla (centipede)  External segmentation distinct  Tagmata: head and trunk  Head: 1 pair of antennae; mandibles; 2 pairs of maxillae  Trunk: with only 12 pairs of legs; most segments with 1 pair of legs, some without legs  Gonopore: unpaired, on segment 4 of trunk in front of legs Class Diplopoda (millipede)  External segmentation plainly evident  Tagmosis not pronounced; distinct head followed by a segment enlarged dorsally (collum) which resembles those of the trunk; latter composed of thorax and abdomen  Thorax poorly differentiated from collum and abdomen; distinguished from latter by the presence of only 1 pair of legs on each of the three segments; legs moved forward on segments 1 and 2  Abdomen, almost all apparent segments with 2 pairs of legs  Gonopore paired, at base of the legs of segment 2 of thorax SIGNIFICANCE OF INSECTS (2 standpoints) 1. Their extreme importance from human point of view, is that… a. they are major rivals for domination  destroy our food both before and after harvest  damage the wooden structures of our houses  transmit causal organisms of our most devastating diseases  direct attacks causes irritation, blood loss and even death 54 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  b. also, insects are vital to our survival on earth  pollinate our crops  control many of our pests  return much of our waste to the soil  source of honey, beeswax, silk, shellac, cochineal dye  serve as food for man and as feed to domesticated animals 2. Their tremendous success relative to the organisms other than humans is apparent in the a. number of extant species and their abundance  1 – 3 M identified species (general estimate is 750,000 species)  outnumber all other species of animals and all species of plants combined  most impressive example of insect abundance __ locust swarms (several billions consume 3,000 tons of food daily)  with regards span of geologic time traversed by group of organisms in evolution, insects are relatively ancient, i. e. Collembola is represented in Devonian era (400 M years ago), which is the same as the first vertebrates, while mammals appeared only 230 M years ago; even cockroaches, grasshopper and dragonflies occurred in the Carboniferous Era which is at least 300 M years ago; thus insects, ruled the air for 100 M years (i. e. as the only flying animals) b. adaptability to various environmental conditions; they are organisms with extreme structural and functional diversity Note: Throughout, insects have proved to be phenomenally successful. Their biological design (basic winged form), remaining unchanged is the reason for their significance. WHAT IS IT ABOUT THE BIOLOGICAL DESIGN THAT HAS MADE INSECTS SO SUCCESSFUL? IS IT...  Possession of rigid impermeable exoskeleton?  Ability to fly?  High reproductive potential?  Small size?  Adaptation of behavior, physiology, biochemistry to changing conditions?  Varied developmental stages and types of development? PROBABLY, ALL THESE THINGS AND MANY MORE... Entomology | 55 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Entomology Defined  Entomology is the scientific study of insects and related arthropods (Ross and Jacques, 1981). Specialized Fields in Entomology  Insect Morphology: deals with the study of comparative anatomy and the development of an insect’s form and structure  Insect Physiology: science which deals with the study of the physical and chemical changes in the insect body or the functions of the forms and structures  Insect Ecology: study of insect which deals with the interrelationship to its environment  Insect Toxicology: deals on the study of how chemical drugs in agriculture and medical practices affect the life of insects  Forest Entomology: deals with the study of the insect communities in the forest ecosystem  Medical Entomology: deals with the study of insects that parasitize man and domesticated animals, those that serve as vector of human and animal diseases  Economic Entomology: the part of the science that deals with the species that is actually or potentially important in beneficial or injurious manner. History of Philippine Entomology The development of Philippine Entomology was recorded (in 1981) by the late Dr. Bernardo P. Gabriel (Philippine Entomologist vol. 4(6): 495-501), a distinguished professor of the Department of Entomology, College of Agriculture, University of the Philippines at Los Baños. His accounts cover the period of the first recognizable written record of the Philippine insect to the 70’s. He subdivided this span of time into 5, namely:  Spanish Period (1521 – 1899: 6th –19th Century)  Early American Occupation (1900 – 1920)  Rise of the Filipino Entomologists (1922 –1940)  War Setback and Rebuilding (1941 – 1960) 56 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)   Developments and Directions in the Sixties and Seventies (1961 – 1979). Spanish Period (1521 – 1899; 16th – 19th Century) YEAR MILESTONE 1521 Pigafetta’s account of Palawan leaf insects __ the first recognizable written record of a Philippine insect 1569 Earliest recorded account of locust swarm in the Philippines (Panay Island) 1593 Spanish Priest Padre Antonio Sedeno first planted mulberry and introduced sericulture in the Philippines. 1616 Philip III of Spain promulgated laws of the Indies which prescribed the work of churchmen, secular persons and the Royal Treasury in connection with the extermination of locusts. Similar decrees were promulgated in the following years __ 1774, 1819, 1858, 1866 and 1888. 1642 Ordinances of Good Government promulgated by Governor-General Don Sebastian Hurtado de Corcuera _ revised by Governor General Don Fausto Cruzat y Gongora 1696 _ Ordinance provide that men and women must be made to destroy locust under penalties imposed for neglect. Quota _ so many gantas of locust destroyed. Punishment for Alcalde _ Mayor and Corregidor shall be deposition from office and change in their residences. 1780 Augustinian Missionary Father Manuel Galliana introduced sericulture for the second time. 1781 Economic Society of Friends of the country (Sociedad Economico de los Amigos del Pais) founded by Governor Jose Vasco y Vargas endeavored to promote sericulture in the Camarines (part of the plan to encourage agricultural production including tobacco, cotton, spices and sugar cane). 1816 Johann Friedrich Eschscholtz _ Russian entomologist; first entomological investigator to visit the Philippines on the Russian Ship Rurik. 1826 Cochineal insect was first introduced and again in 1861, but did not succeed. 1830 Opening of the port of Manila to the world’s commerce _ Foreigner other than Spaniards were allowed to enter the country including foreign explorers. 1831 Hugh Cuming _ English conchologist collected in many parts of Luzon resulting in the publication of some important Philippines insects, e.g. Promecotheca cumingii (Baly) 1858. 1837 Westwood, J. O. published characteristics of new insects from Manila, collected by Mr. Cuming _ Proc. Zool. Soc. London 5:30. 1848 German savant Hans HermanBehr stayed in the Philippines for two years collecting insects specifically Lepidoptera. 1849 Successful introduction of a starling, locally known as “Martinez” _ Aetheopsar cristatellus Linn. From Southern Chinato control locust. First attempt at biological control of insects in the Philippines. Entomology | 57 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1851 Earliest known species of Philippines Hemiptera published by W. S. Dallas derived from Cuming’s material which got into the British Museum. 1856, 1862 Pierre Joseph Michael Lorquin, famous French entomologist visited the Philippines and also worked on Lepidoptera. 1859 – 1865 The German entomologist, Carl Semper, collected insects in different localities in the Philippines which resulted in several publications on Philippines insects especially by his brother, George Semper. 1868 Brauer described Philippine Neuroptera and Libellulidae (Odonata). 1870 Hemiptera Insularum Philippinarum published by Carl Stal _ famous Swedish entomologist (Father of Modern Hemipterology) _ From materials collected by Carl Semper. 1870-1871 Earliest report on Philippine Hymenoptera by F. Smith. 1875 Candeze _ Belgian entomologist first described Philippine Elaterids (Coleoptera). 1877 Stal published _ Orthoptera Nova ex Insulis Philippines _ first report on Philippine Orthoptera also derived from Semper’s collection. French baron Edmond de Selys Longchamps first report on Odonatainthe Philippines _ also published more on Odonata in 1891. 1882 C. R. Osten-Sacken first report on Diptera from the Philippine Islands brought home by Dr. Carl Semper. 1885 Ramon Jordana’s Bosquejo geografica e historico-natural del archipelago Filipino published in Madrid _ a general work on Zoology which included insects, the first of its kind by a resident worker. 1886 – 1892 George Semper, brother of Carl Semper, German entomologist published Die Schmitterlings der Philippinischen der inseln; Rhopalocera. First extensive publication on Philippine Lepidoptera. 1890 Domingo Sanchez y Sanchez _ assistant zoologist in the Government Forestry Service _ published a paper on the coffee longhorn borer _ this is the first published biological study of the insect pest. 1891 Odonates des Philippines by French Baron de Selys-Longchamps. 1894 – 1896 Boletin Oficial Agricola de Filipinas _ monthly issue on Agronomica Service _ contains general articles on insects of economic importance. 1894 Jose Sanchez first study on the white grub, Leucopholis irrorata, as published on monthly issue of the Agronomical Service. 1895 Francisco Alvarez _ ecology and control of migratory locust _ first comprehensive description on locust ecology. 1895 – 1896 Publication of Dominican Father Castro de Elera _ Catalogo sistematico de toda lafauna de Filipinas conocida hasta el presente (3 volumes) _ an extensive work on Philippine Fauna which included several pages on Philippine insects _ this is one of the two works done by local residents during the period. 58 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1896 Baer Catalogue of Philippine Coleoptera. Also from Semper Collection. 1896 – 1902 George Semper’s second publication on Philippine Lepidoptera: Heterocera both milestones in Philippine entomology. 1899 Lepidopteran der Inseln Palawan by Otto Staudinger who sent collectors to the Philippines for materials in this publication Additional Notes Towards the end of the 19 th century, resident collectors appeared in the persons of Alexander Schadenberg (one of the German founders of Botica Boie), Regino Garcia, Francisco Sanchez, S. J., Ateneo professor and his pupils Jose Rizal and Drs. Leon and Luis Guerrero. None of them published but placed their collections on the hands of foreign specialists. Early American Occupation (1900 – 1920) YEAR MILESTONE 1902 Bureau of Agriculture organized. Control of migratory locust became one of its important activities. First time that a microbial agent, a fungus, was used for the control of migratory locust. Charles S. Banks _ an American, was the first government entomologist in the Philippines _ published on various aspects of economic entomology (including medical entomology and systematics). Also organized entomology section in the Bureau of Government Laboratories (late Bureau of Science, recently National Institute of Science and Technology. Later became Department Head, Entomology Department, UPCA. 1903 – 1905 Father William A. Stanton and Father Robert E. Brown as sideline to their regular duties in Manila Observatory published various notes on insects in the monthly bulletin of the Weather Bureau. 1904 Pests of cacao published by Banks. 1906 Founding of the Philippine Journal of Science where most of the taxonomic work on Philippine insects were published especially during the early American period. 1907 Philippine Agricultural Review (later Philippine Journal of Agriculture (1930) now Journal of Plant Industry (1963) founded. Most of the applied work in entomology of the Bureau of Agriculture were published in this journal. 1908 First extensive publication on mosquitoes of the Philippines by C. Ludlow. 1909 Department of Entomology established with the U.P. College of Agriculture. First headed by E. M. Ledyard. D. D. Mackie _ Chief entomologist of the Plant Pest Section of the Bureau of Agriculture tested arsenical sprays for plant pest control. 1910 Entomology section of the Bureau of Agriculture organized. Plant Industry Division first headed by C. R. Jones and then succeeded by D. B. Mackie. Entomology | 59 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1911 Philippine Agriculturist and Forester founded where entomological findings by staff of the Department of Entomology at UPCA were published. F. O. Cevallos _ presented on of the earliest works on the use of chemicals for pest control in this country. Insecticides tested were kerosene emulsion, Resin wash, Bordeaux mixture, white arsenic, carbon bisulphide. 1912 Second Philippine Legislature ended the first Plant Quarantine Law, Act No. 2145. Arrival of Charles F. Baker in the Philippines. Baker, who became Dean of the College of Agriculture, UP in 1917. With the aid of the Cuban collector, Julian Valdez, whom he paid out of his personal funds did more than any other individual to augment our knowledge of Philippine insect fauna. He collaborated with 115 world authorities resulting in the publication of 400 papers on Philippines insects. 1913 Mitzmain, M. S., found that surra, a disease of carabao is striated, transmitted by the common housefly, Tabanus stratus Fabricius. Mitzmain was the first to establish veterinary entomology in the country. Beekeeping using imported Italian bees first attempted in the Philippines _ C. H. Schultz. 1915 Locust Act No. 2472 _ enacted. This act conferred on the Bureau of Agriculture the power of directing and supervising the locust campaign all over the country. First Filipino instructor in entomology _ Leopoldo B. Uichanco. 1916 – 1917 Catalogue of Philippine Coleoptera by W. Schultz published. 1917 Mackie developed a process of fumigating cigars in partial vacuum to destroy beetles. Introduction of Scolia manilae into Hawaii by Muir. 1918 L.B. Uichanco _ first Filipino M. S. in entomology UPCA. Otanes _ elucidated biology of the beanfly _ still a serious pest of legumes. 1919 Plant Pest Section became a separate division of the Bureau of Agriculture _ with Gonzalo Merino as the first chief. This was reorganized into 3 sections in 1924, namely: Plant Quarantine, Entomology and Plant Pathology. 1921 (April 21) Hawaii Sugar Planter’s Association donated PhP4,000.00 to the University to be utilized in the erection of an insectary in Los Baños for furthering entomological work in the Philippines. First donation to the University from a private source. 1921 – 1922 Woodworth, H. E. _ published the first comprehensive host-index of insects injurious to Philippine crops. 60 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Rise of the Filipino Entomologists (1922 - 1960) YEAR MILESTONE 1922 Uichanco, Leopoldo B. _ first Filipino to obtain a doctoral degree in entomology. Uichanco described new species of Psyllids _ first Filipino to describe Philippine insects. Cendana reported biology of banana weevil, a serious pest of banana in the country. 1923 Use of soap as an effective contact insecticide for the control of migratory locust. Soft yellow laundry soap found most effective. Introduction of Opius humilis to control melon fly. 1924 (March 8) Locust Scouting Act (Act 3163) was passed by the Philippine Legislature which provided PhP100,000.00 to locate and fight locusts _ later superceded by other acts to include other pests. 1925 First time airplane was utilized in the control of migratory locust. 1926 Report of G. O. Ocfemia on the transmission of the bunchy top of abaca virus by an aphid Pentalonia nigronervosa. First report of insect transmission of a plant virus in the country. Insecticidal properties of Derris in the Philippines by Castillo. 1927 Use of Paris green as larvicide for mosquitoes by Manalang. 1928 – 1929 Introduction of biocontrol agents by UPCA, Dept. of Entomology. 1928 Distribution of life in the Philippines by Rickerson et al. recorded the number of insects found in the Philippines at that time. 1929 Biology of the corn borer _ Ostrinia furnacalis, still the most serious pest of corn in the country was studied by C. Bulligan. Studies on the effect of dry heat on weevils in corn and corn seed by E. M. Paller. Dammerman’s Agricultural Zoology of the Malay Archipelago included unpublished data of Philippine insects from the Department of Entomology. 1931 De Mesa _ Wood borer and lumber industry. The Makiling Echo. 10(1): 15-19. First report on forest insects. Extensive biological studies of the white grub Leucopholis irrorata done separately by Uichanco and Otanes. 1932 Mutation studies on Philippine wild Drosophila by Clemente. 1933 First study on pesticide residue _ amount of residual arsenic on vegetable crops dusted and sprayed with arsenicals _ J. N Samson. 1934 – 1935 Forest host plants of injurious insects in the Philippines. The Makiling Echo 13(4): 245-250; 14(2): 93-99 by De Mesa. 1934 & 1936 Russel and Baisas published the first illustrated key to the Philippine Anopheles Entomology | 61 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1934 First report on mites of crop plants in the Philippines by Fajardo and Bellosillo. Cendana, first Filipino trained in biological control of insects. 1936 Uichanco theory on locust outbreaks in relation to sun spot cycle. 1939 Report on the ecology of probable outbreak center of migratory locust by Uichanco. 1941 Viado, first insecticide toxicologist in the Philippines. War Setback and Rebuilding (1941 – 1960) YEAR MILESTONE 1946 Introduction of organic insecticides in the Philippines with DDT used against houseflies and migratory locust. 1947 Cendana and Baltazar reported on the cotton leafhopper _ Empoasca bigutulla. First published report on entomology after World War II. C. R. Baltazar, first Filipina with college degree major in entomology. Committee headed by Dr. S.M. Cendana to look into the postwar activities of Philippine entomology. 1949 Phil. Agriculture Vol. 1 _ by Uichanco and Sacay. Contain information on Philippine insect pests of crops. 1951 Checklist of ants of Asia by Chapman and Capco. 1952 U.P. Los Baños _ Cornell contract started with three American visiting professors detailed in succession from 1954 to 1959 at the Department of Entomology (J. G. Mathyssee, R. W. Dean and B. V. Travis) _ Work were largely on economic entomology specifically chemical control. Young Filipinos were sent for graduate training abroad (1954 – 1960). 1954 First studies conducted on plant resistance to insects by S. M. Cendana _ using corn hybrid, and inbred strain against corn earworm and corn borer. 1959 Extensive bibliography of Philippine entomology compiled for the first time by R. M. Ela. A list of plant pests of the Philippines with special reference on field crops, fruit trees and vegetables by S. R. Capco. Developments and Directions in the 60’s and 70’s (1961 – 1979) YEAR MILESTONE 1960 Entomology research in the Philippines further boosted especially on insects affecting rice with the establishment of the International Rice Research Institute. 1961 L. C. Rimando, first Filipino acarologist spearheaded research on mites in the Philippines. 62 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1962 July 22 _ Founding of the Philppine Entomological Society (now Philippine Association of Entomologists, Inc.), the first entomological organization in the Philippines with S. M. Cendaña as the first President. 1964 B. P. Gabriel, first Filipino insect pathologist. International Symposium on the major insect pests of the rice pest by the International Rice Research Institute. 1966 Publication of the Catalogue of Philippine Hymenoptera (with a bibliography 1758 – 1963) by C. R. Baltazar. The first catalogue of a major insect order done by a Filipino. Delfinado published the first monographic treatment of Philippine mosquitoes except Aedes. 1967 First National Meeting of the Philippine Association of Entomologists held at the U.P. College of Agriculture _ August 12. First National Symposium in Philippine Entomology _ Nov. 25. 1968 Founding of the Philippine Entomologist, the first journal of entomology in the Philippines by the Association of Philippine Entomologists (L. C. Rimando, first editor). 1970 Illustrated keys to the Anopheles mosquitoes of the Philippine islands by Cagampang and Darsie. A comprehensive key on the important group of insects of medical importance. 1971 Mosquito Fauna of the Philippines by R. G. Basio _ An extensive treatment on all mosquito species reported in the Philippines with notation on the bionomics and vector status of each species. 1976 National Crop Protection Center founded with Dr. F. F. Sanchez as first Director. 1978 First Regional Meeting of the Philippine Association of Entomologists in Davao City _ February 17. These developments led to what entomology is today in the Philippines. External Insect Morphology The Insect's Head In most insects, the head capsule is a sturdy compartment that houses the brain, a mouth opening, mouthparts used for ingestion of food, and major sense organs (including antennae, compound eyes, and ocelli). Embryological evidence suggests that the first six body segments (three pre-oral and three post-oral) of a primitive worm-like ancestor may have fused to form the head capsule of most present-day insects. Entomology | 63 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  The surface of the head is divided into regions (sclerites) by a pattern of shallow grooves (sutures). The uppermost sclerite (dorsal surface) of the head capsule is known as the vertex. A coronal suture usually runs along the midline of the vertex and splits into two frontal sutures as it extends downward across the front of the head capsule. The triangular sclerite that lies between these frontal sutures is called the frons. The epistomal suture is a deep groove that separates the base of the frons from the clypeus, a rectangular sclerite on the lower front margin of the head capsule. The genae ("cheeks") are lateral sclerites that lie behind the frontal sutures on each side of the head. Below each gena there may be another sclerite (the subgena), separated from the gena by a subgenal suture. A pair of compound eyes, sockets for two antennae, and one or more ocelli (simple eyes) also may be found on the front, top, or sides of an insect's head. Near the back of the head, an occipital suture circumscribes the head capsule at the posterior margin of the vertex and genae. This suture marks the location of an internal sclerotized ridge (apodeme) that strengthens this part of the head capsule. Just behind the occipital suture lie the occiput and postgenae, tiny sclerites that are probably remnants of the fifth primitive segment that fused to form the insect's head. At the posterior-most margin of the head, a vestige of the sixth primitive segment is marked by a faint postoccipital suture and a thin, band-like sclerite (the postocciput) that adjoins the neck membrane. The insect's neck is known as the cervix. This is a membranous area that allows considerable freedom of movement for protraction and retraction of the insect's head. The cervical membrane extends from the posterior portion of the postocciput to the prothorax, and it represents a transitional zone between the head and thorax. Small cervical sclerites serve as points of attachment for muscles that control head movements. Eyes 64 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  Insects have two kinds of eyes: the compound eyes and the simple eyes or ocelli (singular, ocellus). Most adults and many nymphs have large, prominent compound eyes that give insects a broad visual field. Many adult insects and larvae as well as immatures of hemimetabolous insects have dorsal ocelli in addition to compound eyes. The ocelli appear to enhance light detection by the compound eyes and to register cyclical changes in light intensity that correlate with diurnal behavioral rhythms. The compound eyes, located on each side of the head, consist of many hexagonal elements called facets or corneal lenses. These facets number from only a few as in the springtails to as many as 28,000 as in the dragonflies. Each lens represent the outer portion of a single eye element or ommatidium. Sometimes the upper facets are much larger than the lower and occasionally, the eyes are divided into separated dorsal and ventral parts. They may show a pattern of bands or patches of contrasting colors in life. The interfacetal junctions are often provided with fine hairs which may be dense enough to give the eyes a distinctive appearance. Three ocelli, typically arranged in an isosceles triangle on the vertex, are present in so many insects. Each lateral (or posterior) ocellus has a single lens, but differs from an ommatidium of a compound eye in that the lens covers a number of internal eye elements. The median ( or anterior) ocellus was apparently formed from two separate ocelli which became fused together, and it is innervated from both sides of the deutocerebrum. Vision in insects is based on the Theory of Mosaic Vision. Each facet of the compound eye accommodates only that part of the image projected at a specified angle from the object. The entire vision depends on a simultaneous functioning of all facets in which the image is perceived. If some of these facets are damaged, the object as seen by the insect will have missing parts corresponding to the loss of vision due to the nonfunctional lenses. Antennae The antennae are a pair of sense organs located near the front of an insect's head capsule. Although commonly called "feelers", the antennae are much more than just tactile receptors. They are usually covered with olfactory receptors that can detect odor molecules in the air (the sense of smell). Many insects also use their antennae as humidity sensors, to detect changes in the concentration of water vapor. Mosquitoes detect sounds with their antennae, and many flies use theirs to gauge air speed while they are in flight. Although antennae vary widely in shape and function, all of them can be divided into three basic parts: Entomology | 65 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  1. scape -- the basal segment that articulates with the head capsule. It contains intrinsic muscles and is generally larger than the other segments 2. pedicel -- the second antennal segment; nearly always contain a sensory organ called Johnston organ which respond to the movement of the distal part of the antennae relative to the pedicel. 3. flagellum or clavola -- all the remaining "segments" (individually called flagellomeres); multisegmented but may be reduced or variously modified. The antennae may be reduced or absent in some larval insects. The details of the clavola are useful in differentiating between some representative groups of insects and sometimes between male and female of the same species. Types of Antennae Name/Description Appearance Example(s) Setaceous (bristle- like) – segments becoming more Dragonflies slender dorsally Filiform (thread-like) - Ground beetles segments nearly uniform and in size, usually cylindrical Cockroaches 66 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Moniliform (bead-like) - segments similar in size, Termites more or less cylindrical Serrate (saw-toothed) - segments particularly the Female giant click beetle distal half, more or less triangular Clavate (gradually clubbed) - segments Butterflies gradually increase in size Capitate -- abruptly Carrion beetles clubbed Lamellate -- nested plates Scarab beetles Entomology | 67 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  Pectinate (comb-like) - Fire-colored beetles, most segments with long, Male glow-worms and slender lateral processes Male giant click beetles Plumose (brush-like or feathery) - segments with Male mosquitoes whorls of long hairs Geniculate (elbowed) - first segment long, following segments small Bees and Ants and going at an angle to the first Aristate (pouch-like with usually dorsal bristle) - Houseflies last segment usually Syrphid flies enlarged and bearing a conspicuous arista Stylate - the last segment bearing an elongate terminal finger-like Robber fly process called style Mouthparts 68 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Mouthparts are some of the most distinctive features of insects and their structure tells a great deal about the feeding habits of a species. In all insects the mouthparts have evolved from a basic or primitive type (chewing type) exemplified by the grasshopper. Mouthparts are greatly varied, but their primitive form include a labrum (upper lip), a pair of chewing mandibles (jaws), a pair of maxillae (second jaws), and a labium (lower lip). These structures surround the mouth and form the pre-oral cavity. In addition, a central tongue-like hypopharynx drops from the membranous floor of the cranium, behind the mouth, and bears the opening of the salivary ducts. The general description of the structures are based on the mouthparts adapted for biting and chewing as follows: The labrum is normally a movable plate attached to the lower margin of the clypeus with its outer surface generally strongly sclerotized and its distal margin sharply defined. The interior or ventral surface of the labrum, called epipharynx, is membranous and equipped with small tactile hairs and taste organs. A pair of small sclerites, the tormae, may be present at the basolateral angles of the labrum. The labrum forms the roof of the pre-oral cavity and the mouth and covers the base of the mandibles. The mandibles are a pair of strongly sclerotized, unsegmented jaws situated immediately posterior to the labrum. Except in Archeognatha, the mandibles primitively articulate with a process of the clypeus anteriorly by a ginglymus (hinge) joint and with the gena posteriorly by a condyle (ball). The mandibles move sideways and are operated by the most powerful muscles in the head. The mandibles are the principal feeding organs, being used primitively to bite off and chew food. The maxillae are paired segmented structures, lying posteroventral to the mandibles and anterodorsal to the labium. The basal segment, the cardo, is attached to the head proximally and to a longer 2nd segment, the stipes, distally. The stipes bear two lobes, the lateral galea and the mesal lacinia. Attached laterally to the distal part of the stipes is the usually1 – 7 segmented maxillary palps or palpus. Sometimes, the galea is 2- segmented and the lacinia may be spined or toothed on its mesal border. The maxillae serve as accessoty jaws. The laciniae help to hold the food when the mandibles are extended and also assist in mastication. The galea and palp assist in selecting the food by touch and taste. The labium consists of the fused 2 nd maxillae. It is attached to the ventral surface of the cranium, bilaterally symmetrical and divided into the postmentum proximally; prementum more distally; 2 distal processes articulated to the prementum on each side, the glossa mesally and paraglossa laterally; and a pair of 1 – 4 segmented labial palps arising from a lateral part of the prementum which is sometimes differentiated as Entomology | 69 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  the palpiger. When the prementum is divided transversely into 2 parts, the distal portion bearing the glossae and paraglossae is known as the ligula. The hypopharynx is a median, unpaired, tongue-like organ projecting forward from the back of the pre-oral cavity and dividing it into a dorsal cibarium serving as a food pouch, and a ventral salivarium where the salivary ducts open. The primitive hypopharynx has an elaborate complement of sclerites and bear a pair of lateral lobes called superlinguae. The mouthparts in insects are variously modified. In addition to the chewing type of mouthparts, insects have types that include piercing-sucking, rasping-sucking, siphoning, sponging and chewing lapping. The type of mouthparts an insect possesses determines how it feeds and what sort of damage it inflicts to its host. The piercing-sucking mouthparts are very common among insects. The mouthparts are modified to pierce the epidermis of plants or the skin of animals and to suck up sap or blood. This type is characterized by the presence of a tubular, usually jointed beak enclosing several needle-like stylets. In plant feeders such as the aphids and whiteflies (Homoptera) the piercing-sucking needle is formed from 4 hairlike stylets fitted closely together. The outer stylets are derived from mandibles and the inner ones from the maxillae. The maxillary stylets are double-grooved on the inner side. When held together, they form 2 channels. One of the channels serve as passage of saliva into the plant to facilitate food flow and digestion. The other channel is used for the uptake of plant juices. The labium forms a protective sheath for the stylets. In blood-feeding insects like mosquitoes (Diptera) there are 6 stylets. The stylets are formed from the mandibles and maxillae and an additional pair is modified from the hypopharynx and labrum-epipaharynx which forms a food channel. The stylets are enclosed by a protective sheath formed from an elongated labium. The back of the food channel is closed by the hypopharynx with its salivary duct which carries saliva containing enzymes and anticoagulants that reduce blood clotting in the host and improve the flow of blood into the mosquito. The maxillary and mandibular stylets work together as a needle to penetrate the host’s skin. The rasping-sucking mouthparts, characterized as a short, stout, assymetrical conical structure located ventrally at the rear of the head, are a primitive form of the piercing- sucking type. These are found in thrips (Thysanoptera). The mouthparts have a cone- shaped beak formed from the clypeus, labrum, parts of the maxillae and the labium. The beak contains the maxillae, hypopharynx and the left mandible which together form a stylet. The thrips use the beak to make superficial wounds on the host tissues and take up liquid food through the stylet. The siphoning mouthparts are a highly specialized type, modified for the uptake of flower nectar and other liquids. This type is found in practically all adult moths and butterflies (Lepidoptera). The galea of the maxillae are greatly elongated and joined to 70 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  form a slender hollow tube called proboscis through which food passes and held in coiled-spring fashion when not in use. The proboscis is not capable of piercing tissues except in rare instances. Feeding is accomplished by uncoiling the tube and projecting its tip into exposed liquid such as nectar and then sucking up through the food channel running full length through the proboscis. The mouthparts of a common housefly represent the sponging type of mouthparts which are also highly specialized structures. The mandibles and the maxillae are nonfunctional and the remaining parts form a proboscis whose end is expanded into a fleshy lobe with a series of furrows or tiny channels called labella. Liquid food is “mopped up” by the capillary action of the fleshy lobe acting like a sponge. If food is not liquid, salivary secretions through the mouthparts make it so. In the chewing-lapping mouthparts like in the bees and wasps ((Hymenoptera), the mandibles and the labrum are similar to the chewing type and are used for grasping prey, molding wax and manipulating nest materials. The maxillae and the labium developed into a series of flattened elongated structure forming a sort of a lapping tongue through which saliva is discharged and nectar is drawn up as the bee probe deep into the blossoms. The Thorax The second (middle) tagma of an insect's body is called the thorax. This region is almost exclusively adapted for locomotion -- it contains three pairs of walking legs and, in many adult insects, one or two pairs of wings. Structurally, the thorax is composed of three segments: prothorax, mesothorax, and metathorax. These segments are joined together rigidly to form a "box" that houses the musculature for the legs and wings. Each segment has a dorsal sclerite, the notum (pronotum, mesonotum, and metanotum) which may be further subdivided into an anterior scutum and a posterior scutellum. The ventral sclerite of each segment is the sternum (prosternum, mesosternum, and metasternum). The side of each segment is called the pleuron -- it is usually divided by a pleural suture into at least two sclerites: an anterior episternum and a posterior epimeron. The pleural suture marks the location of an internal ridge of exoskeleton (an apodeme) that strengthens the sides of the thorax. Ventrally, this apodeme forms a point of Entomology | 71 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  articulation with the basal leg segment (the coxa). In thoracic segments that bear wings, the pleural apodeme runs dorsally into the pleural wing process, a finger-like sclerite that serves as a pivot or fulcrum for the base of the wing. Legs Most insects have three pairs of walking legs -- one pair on each thoracic segment. Each leg contains five structural components (segments) that articulate with one another by means of hinge joints: 1. Coxa 2. Trochanter 3. Femur 4. Tibia 5. Tarsus The term pretarsus refers to the terminal segment of the tarsus and any other structures attached to it, including: ungues -- a pair of claws arolium – a lobe or adhesive pad between the claws empodium -- a large bristle (or lobe) between the claws pulvilli -- a pair of adhesive pads at the base of the claws Normally, all three pairs of legs are used for running and walking. The middle legs usually remain relatively simple in structure but the fore and hind legs may become extremely modified and specialized to fit the mode of life of the insect. Leg Adaptations and Striking Modifications Type/Characteristic Appearance Example(s) Ground beetles Cursorial/gressorial (adapted for and running and walking) Cockroaches 72 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Raptorial (adapted for catching and grasping prey) - forelegs Praying mantids armed with sharp opposing spines and spurs Natatorial (adapted for Diving bugs swimming)- segments of forelegs and flattened and with long hairs Water beetles Fossorial (adapted for digging in soil) - forelegs with scraper- like Mole crickets parts Saltatorial (adapted for jumping) Grasshoppers - enlarged hind femur Assembling/pollen gathering leg - hind tibiae with hairs (pollen Bees basket) Clinging leg - the end of the tarsus of prothoracic leg is a Lice hook-like structure used for clinging to host Wings Functional wings exist only during the adult stage of an insect's life cycle. The wings develop embryologically as evaginations of the exoskeleton -- they may be membranous, parchment-like, or heavily sclerotized. Most insects have distinct two pairs of wings -- one pair on the mesothorax and one pair on the metathorax (never on the prothorax). Entomology | 73 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  Wings serve not only as organs of flight, but also may be adapted variously as protective covers (Coleoptera and Dermaptera), thermal collectors (Lepidoptera), gyroscopic stabilizers (Diptera), sound producers (Orthoptera), or visual cues for species recognition and sexual contact (Lepidoptera). In most cases, a characteristic network of veins runs throughout the wing tissue. These veins are extensions of the body's circulatory system. They are filled with hemolymph and contain a tracheal tube and a nerve. In membranous wings, the veins provide strength and reinforcement during flight. Wing shape, texture, and venation are quite distinctive among the insect taxa and therefore highly useful as aides for identification. Wing adaptations and modifications: Characteristic Appearance Order(s) Elytra -- hard, sclerotized front Coleoptera wings that serve as protective and covers for membranous hind Dermaptera wings Hemelytra -- front wings that are leathery or parchment-like Hemiptera: at the base and membranous Heteroptera near the tip Tegmina -- front wings that are Orthoptera, completely leathery or Blattodea, parchment-like in texture and Mantodea 74 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Halteres -- small, knob-like hind wings that serve as Diptera gyroscopic stabilizers during flight Fringed wings – margins of slender front and hind wings Thysanoptera with long fringes of hair Hairy wings -- front and hind Trichoptera wings clothed with setae Scaly wings – membranous front and hind wings covered Lepidoptera with flattened setae (scales) Hamuli -- tiny hooks on hind wing that hold front and hind Hymenoptera wings together Entomology | 75 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Frenulum -- Bristle near base of hind wing that holds front Lepidoptera and hind wings together The Abdomen An insect's abdomen is the third functional region (tagma) of its body; the abdomen is located just behind the thorax. In most insects, the junction between thorax and abdomen is broad, but in some groups, the junction is very narrow (petiolate) giving the appearance of a "wasp-waist". Entomologists generally agree that insects arose from primitive arthopod ancestors with eleven-segmented abdomens. Some present-day insects (e.g. silverfish and mayflies) still have all of these segments (or remnants of them), but natural selection in more advanced (or specialized) groups has contributed to a reduction in the number of segments -- sometimes to as few as six or seven (e.g. beetles and flies). 76 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Each segment of the abdomen consists of a dorsal sclerite, the tergum, and a ventral sclerite, the sternum, joined to one another laterally by a pleural membrane. The front margins of each segment often "telescope" inside the sclerites of the preceding segment, allowing the abdomen to expand and contract in response to the actions of skeletal muscles. In many adult insects, there is a spiracle (opening to the respiratory system) near the pleural membrane on each side of the first eight abdominal segments. Some spiracles may be permanently closed, but still represented by a dimple in the sclerite. At the very back of the abdomen, the anus (rear opening of the digestive system) is nestled between three protective sclerites: a dorsal epiproct and a pair of lateral paraprocts. A pair of sensory organs, the cerci, may be located near the anterior margin of the paraprocts. These structures are tactile (touch) receptors. They are usually regarded as a "primitive" trait because they are absent in the hemipteroid and holometabolous orders. The insect's genital opening lies just below the anus: it is surrounded by specialized sclerites that form the external genitalia. In females, paired appendages of the eighth and ninth abdominal segment fit together to form an egg- laying mechanism called the ovipositor. These appendages consist of four valvifers (basal sclerites with muscle attachments) and six valvulae (apical sclerites which guide the egg as it emerges from the female's body). In males, the genital opening is usually enclosed in a tube-like aedeagus which enters the female's body during copulation (like a penis). The external genitalia may also include other sclerites (e.g. subgenital plate, claspers, styli, etc.) that facilitate mating or egg-laying. The structure of these genital sclerites differs from species to species to the extent that it usually prevents inter-species hybridization and also serves as a valuable identification tool for insect taxonomists. Other abdominal structures may also be present in some insects. These include:  Pincers -- In Dermaptera (earwigs), the cerci are heavily sclerotized and forceps- like. They are used mostly for defense, but also during courtship, and sometimes to help in folding the wings.  Median caudal filament -- a thread-like projection arising from the center of the last abdominal segment (between the cerci). This structure is found only in "primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera). Entomology | 77 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)   Cornicles -- paired secretory structures located dorsally on the abdomen of aphids. The cornicles produce substances that repel predators or elicit care-giving behavior by symbiotic ants.  Abdominal prolegs -- fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera).  Sting -- a modified ovipositor, found only in the females of aculeate Hymenoptera (ants, bees, and predatory wasps).  Abdominal gills -- respiratory organs found in the nymphs (naiads) of certain aquatic insects. In Ephemeroptera (mayflies), paired gills are located along the sides of each abdominal segment; in Odonata (damselflies), the gills are attached to the end of the abdomen.  Furcula -- the "springtail" jumping organ found in Collembola on the ventral side of the fifth abdominal segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its "cocked" position.  Collophore -- a fleshy, peg-like structure found in Collembola on the ventral side of the first abdominal segment. It appears to maintain homeostasis by regulating absorption of water from the environment. Metamorphosis Each time an insect molts, it gets a little larger. It may also change physically in other ways -- depending on the type of metamorphosis it undergoes: ametabola (no metamorphosis), paurometabola (gradual), hemimetabola (incomplete), or holometabola (complete). Ametabolous insects undergo little or no structural change as they grow older. Immatures are called young; they are physically similar to adults in every way except size and sexual maturity. Other than size, there is no external manifestation of their age or reproductive state. The feeding habits of the young and the adult are the same. (Collembolla, Thysanura, Protura, Diplura) Paurometabolous Development 78 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Paurometabolous insects exhibit simple gradual changes in body form during morphogenesis. Immatures are called nymphs. The nymphs and adult are similar in appearance except in size and extent of wing and development of the genitalia. The nymphs possess rudimentary wings or wing pads which develop progressively until they are fully developed and functional in the adult stage. Developmental changes that occur during gradual metamorphosis are usually visible externally as the insect grows, but adults retain the same organs and appendages as nymphs (eyes, legs, mouthparts, etc.). The nymphs and adults have the same feeding habit and type of food and occupy the same habitat. (Hemiptera, Homoptera, Orthoptera, Thysanoptera, Psocoptera, Embioptera, Dermaptera, Isoptera, Arallophaga, Anoplura) Hemimetabolous insects undergo incomplete metamorphosis. The immatures are called naiads, and are aquatic and have gills for respiration. The naiads look differently from the adults which have wings and are terrestrial and winged. The naiads and adults feed on different kind of food. (Odonata, Ephemeroptera, Plecoptera) Entomology | 79 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  Holometabolous insects have immature forms called larvae that look very different from adults. The changes that holometabolous insects undergo are significant. Larvae are "feeding machines", adapted mostly for consuming food and growing in size. They become larger at each molt but do not acquire any adult-like characteristics. When fully grown, larvae molt to an immobile pupal stage and undergo a complete transformation. Larval organs and appendages are broken down (digested internally) and replaced with new adult structures that grow from imaginal discs, clusters of undifferentiated (embryonic) tissue that form during embryogenesis but remain dormant throughout the larval instars. The larval stage is the main feeding stage. The pupal stage does not feed and is quiescent. The adult stage, which usually bears wings, may or may not feed and is mainly adapted for dispersal and reproduction. Sometimes, the feeding habits and type of food of larva and adult are entirely different, e. g., larva of Lepidoptera chews off solid food while adult sucks up nectar, or may be similar as in some beetles.(Neuroptera, Coleoptera, Strepsiptera, Mecoptera, Trichoptera, Lepidoptera, Diptera, Siphonaptera and Hymenoptera) Most larvae can be grouped into one of five categories based on physical appearance. Common Appearance Larval Type Description Examples Name Body cylindrical with short thoracic legs and Moths and Eruciform Caterpillar 2-10 pairs of butterflies fleshy abdominal prolegs Campodeiform Crawler Elongated, Lady flattened body beetle, with prominent lace antennae and/or wing cerci. Thoracic legs adapted for 80 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  running Body robust and June "C"-shaped with beetle, Scarabaeiform White grub no abdominal dung prolegs and short beetle thoracic legs Body long, smooth, and Click cylindrical with beetle, Elateriform Wireworm hard exoskeleton Flour and very short beetle thoracic legs Body fleshy, worm-like. No House fly, Vermiform Maggot head capsule or flesh fly walking legs Pupae can be grouped into one of three categories based on physical appearance: Pupal Common Appearance Description Examples Type Name Developing appendages (antennae, wings, legs, etc.) held tightly against Butterflies Obtect Chrysalis the body by a shell-like and moths casing. Often found enclosed within a silken cocoon. All developing appendages Beetles, Exarate None free and visible externally Lacewings Entomology | 81 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  Body encased within the Coarctate Puparium hard exoskeleton of the Flies next-to-last larval instar LIFE PROCCESSES IN INSECTS Maintenance of Life in Insects Digestive System  composed of buccal cavity, salivary glands and alimentary canal (gut)  made up of a single layer of cell and supporting nerves and tracheoles, suspended in cavity by connective tissue to integument, and muscles to assist digestion and absorption of food (longitudinal and circular)  divided into three, namely the foregut, midgut and hindgut Stomodaeum An insect's mouth, located centrally at the base of the mouthparts, is a muscular valve (sphincter) that marks the "front" of the foregut. Food in the buccal cavity is sucked through the mouth opening and into the pharynx by contractile action of cibarial muscles. These muscles, located between the head capsule and the anterior wall of the pharynx, create suction by enlarging the volume of the pharynx (like opening a bellows). This "suction pump" mechanism is called the cibarial pump. It is especially well-developed in insects with piercing/sucking mouthparts. From the pharynx, food passes into the esophagus by means of peristalsis (rhythmic muscular contractions of the gut wall). The esophagus is just a simple tube that connects the pharynx to the crop, a food-storage organ. Food remains in the crop until it can be processed through the 82 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) remaining sections of the alimentary canal. While in the crop, some digestion may occur as a result of salivary enzymes that were added in the buccal cavity and/or other enzymes regurgitated from the midgut. In some insects, the crop opens posteriorly into a muscular proventriculus. This organ contains tooth-like denticles that grind and pulverize food particles. The proventriculus serves much the same function as a gizzard in birds. The stomodeal valve, a sphincter muscle located just behind the proventriculus, regulates the flow of food from the stomodeum to the mesenteron. Mesenteron. The midgut begins just past the stomodeal valve. Near its anterior end, finger- like projections (usually from 2 to 10) diverge from the walls of the midgut. These structures, the gastric caecae, provide extra surface area for secretion of enzymes or absorption of water (and other substances) from the alimentary canal. The rest of the midgut is called the ventriculus -- it is the primary site for enzymatic digestion of food and absorption of nutrients. Digestive cells lining the walls of the ventriculus have microscopic projections (microvilli) that increase surface area for nutrient absorption. The midgut is derived from embryonic endoderm so it is not protected by an intima. Instead, the midgut is lined with a semipermeable membrane secreted by a cluster of cells (the cardial epithelium) that lie just behind the stomodeal valve. This peritrophic membrane consists of chitin fibrils embedded in a protein-carbohydrate matrix. It protects the delicate digestive cells without inhibiting absorption of nutrient molecules. The posterior end of the midgut is marked by another sphincter muscle, the pyloric valve. It regulates the flow of material from the mesenteron to the proctodeum. Digestion Defined It is a series of activities and hydrolytic reactions (involving enzymes) that convert complex substances (foodstuffs that insect eats like proteins, carbohydrates, fats and lipids) to simpler ones (amino acids, fatty acids, glycerols, sugars) Foregut – has a cuticle with spines (intima), hair or teeth 1. Pharynx – basically for ingestion of food; possess elaborate muscle 2. Esophagous – narrow tube that leads to the crop 3. Crop – dilatation of posterior part of foregut; food storage as well as defensive substances; in some insects, crop may be in the form of a diverticula; main seat of digestion for Orthoptera, Calliphora, Coleoptera and Aphoidea, but for caterpillars, housefly, tse tse fly and Musca, it serves as food storage 4. Cardiac Sphincter – is just an invagination of foregut into midgut; in some, it could be an elaborate structure known as proventriculus, “gizzard” (teethlike); regulates the passage of food from foregut to midgut Midgut – lined with peritrophic membrane 1. Gastric caeca – end of foregut and beginning of midgut Entomology | 83 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  2. Peritrophic membrane – a temporary lining that is delicate and perforated membrane that serves to protect the midgut from particles or food coming from the foregut; secreted by specialized cells in midgut; made-up of protein, chitin and mucopolysaccharides; enclosed foodstuffs go directly to hind gut, thus ensures that midgut cells are protected from abrasions; have goblet cells (modified midgut cells); it may have a purely mechanical effect. NOTE: goblet cells are degenerative cells that help pump out excess potassium from hemolymph 3. Midgut cells classification a. Regenerative – cells involved in production of enzymes and secretion, as well as absorption of digested food b. Degenerative 4. Pyloric sphincter – demarcation line between midgut and hindgut, furnished with muscles to regulate deposition of waste to hindgut Feeding Mechanisms – processes used by insects to secure the food, gain access to, or to select the ingestible parts, modify them if necessary and transfer them into a storage or processing part of the gut. The structures involved are mouthparts and their muscles, salivary system, food pumps, and skeletal and muscular components. Types of Mouthparts 1. Chewing, Cutting 2. Piercing-Sucking 3. Other Modifications Components of Chewing, Cutting Feeding Process 1. The food has to be held or secured relative to the mouthparts. 2. The pieces have to be detached from the food source. 3. The detached pieces have to be further reduced for ingestion. 4. The food particles must be brought to the functional mouth and retained there for swallowing. 5. The particles must be moved from the mouth to the lumen of the gut for digestion and absorption. 6. There should be a lubricating fluid to be applied to the food and mouthparts. Components of Piercing-Sucking Feeding Process - They should be able to penetrate or pierce through protective barriers. 1. Purchase. Mechanical connection with the food source must be made, to allow forces generated by the insect to host penetration by the mouthparts. 2. Initial Puncture. Superficial layers of the food source often differs structurally and mechanically from underlying layers (e.g. bark, skin, seed coats must be penetrated which may demand a specialized structure or apparatus like stylets. 84 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)  3. Deep Penetration. There may be considerable non-nutritive material layer to traverse before liquid food is reached and may mean a different mechanism to be adapted in particular, and may be necessary to allow mouthparts to be protracted for considerable differences, and to be controlled. 4. Recognition of Target. Insect will need appropriate signals to inform the insect when the food has been reached. 5. Uptake of Food. A structure is necessary to convey the food to the mouth of the insect. This food canal may need to resist considerable pressure differences and have a minimal resistance of fluid flow. 6. Pumping. Devices will be needed to create a pressure graedient to supply energy necessary for movement of food along food canal. 7. Lubrication. Saliva or special secretions may be needed to assist penetration of mouthparts either by their lubrication or by chemical breakdown of tissues, to make food material liquid. Devices will be needed to convey the saliva to appropriate site. 8. Sheathing of Mouthparts. Specialized structures are needed to enclose the piercing- sucking mouthparts when not in use or may need mechanical support during deployment. Other Feeding Process Modifications 1. Insects feeding on free liquids (no barrier like nectar, pulp from decaying or rotting food, feces). Insects can drink but others have specialized systems to counteract surface tension and to penetrate flower structures. a. Siphoning – tube-like proboscis for nectar feeding in Lepidopteran adults b. Sponging type in housefly c. Lapping – bee for honey and nectar 2. Catching mobile prey. Dragonfly larvae are aquatic like frogs; the labium has evolved into a hinged extensible device equipped with terminal pincers. 3. Filter feeding for aquatic insects, wherein their feeding mechanisms have evolved in which suspended particles are filtered from water and concentrated before ingestion like fish; for others, they use cuticle, cuticular filters for mosquitoes and black fly larvae while caddis flies have silk nets. Enzymes are proteins that can catalyze reactions and are produced in salivary glands, gastric caeca and midgut cells Saliva –  is a clear, watery neutral fluid that have several functions: 1. moistening of food 2. sugar dissolving 3. moistening of mouthparts and cleaning between feeding 4. for active enzyme constituents  basically composed of amylase and invertase (sucrase) Entomology | 85 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Physiological Adaptations/Specializations 1. Feeding Habits (depending on food source) e.g. siphoning, lapping and filter feeding 2. Presence of Microorganisms in gut which is used for feeding and digestion  Bacterial fermentation chamber in hindgut for wood vegetable and bacteria, stored for weeks, digested and lyzed by midgut, and then nutrients are absorbed from bacteria  Protozoans for cellulose digestion 3. Presence of Fungus Gardens in ants and termites sometimes called “ambrosia gardens” to take care of the young. 4. Stylet Sheaths (aphids, whiteflies, Dysdercus) are produced when insects feed on the rice plants. Saliva is hardened to form stylet sheaths then filtered off to prevent sap to exude to the exterior and thus, stylets are not affected. 5. Filter Chamber. Physical association between foregut and terminal midgut to shorten the distance so that there is no dilution of fluid. The filter chamber aims to remove the fluid as soon as possible as not to dilute the hemolymph and thus easily concentrate the food for digestion. 6. Food Storage. Insects have internal stores in the  Fat body  Insect crop, in termites they have external stores like honeybees in their cell 7. Extraintestinal Digestion. High hyaluronidase in saliva of carnivorous insects and attacks (digest) mucopolysaccharides in connective tissues, and also acts as spreading agents for other enzymes (proteases), once enzyme have acted upon the food substance, they suck liquid.  For plant sucking homopterans, their saliva have pectinase or galacturonidase (enzymes which can digest middle lamella of plant cell wall) thus aid in tissue penetration by stylets  For silkworm, it uses an enzyme from the midgut (protease) that will attack silk so the insect can emerge from the cocoon In blowflies or flesh flies, liquefy meat partially prior to ingestion 8. Digestion of Unusual Food like cellulose, beeswax and keratin. 9. Hematophagous Insects include the blood-sucking hemipterans and dipterans. The diet is highly unbalanced, containing 7% protein and part of this is sequestered in hemoglobin (RBC). The mouthparts are piercing-sucking capable of piercing RBC and therefore liberate hemoglobin. Blood suckers have anti-coagulants and in the case of Glossina, it is identified as Plasminogen activator. Once blood reaches crop, coagulation is rapid and thus it is ready for regular digestion. Excretory System Hindgut – lined with cuticle but more permeable to water; cells are larger, striated and have microvilli  Functions for water, salt and amino acid absorption  Serves as storage for cellulose digestion in termites and Scarabaeid beetles 86 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)   Have respiratory functions in Anisoptera (dragonflies) larvae  Modified into rectal pads for water, amino acid and salt reabsorption Proctodaeum. The pyloric valve serves as a point of origin for dozens to hundreds of Malpighian tubules. These long, spaghetti-like structures extend throughout most of the abdominal cavity where they serve as excretory organs, removing nitrogenous wastes (principally ammonium ions, NH4+) from the hemolymph. The toxic NH4+ is quickly converted to urea and then to uric acid by a series of chemical reactions within the Malpighian tubules. The uric acid, a semi- solid, accumulates inside each tubule and is eventually emptied into the hindgut for elimination as part of the fecal pellet. The rest of the hindgut plays a major role in homeostasis by regulating the absorption of water and salts from waste products in the alimentary canal. In some insects, the hindgut is visibly subdivided into an ileum, a colon, and a rectum. Efficient recovery of water is facilitated by six rectal pads that are embedded in the walls of the rectum. These organs remove more than 90% of the water from a fecal pellet before it passes out of the body through the anus. Embryonically, the hindgut develops as an invagination of the body wall (from ectodermal tissue). Just like the foregut, it is lined with a thin, protective layer of cuticle (intima) that is secreted by the endothelial cells of the gut wall. When an insect molts, it sheds and replaces the intima in both the foregut and the hindgut. 1. Rectal pads – cuticle is thinner and has depressions wherein the epicuticle is also thin; hindgut cells of rectal pads have a lot of folds and mitochondria; membrane stacks are also present to increase surface area for secretory or absorption function 2. Potassium (K) ions – are active electrolytes, responsible for pumping amino acid, salt and water reabsorption back to hemolymph Cryptonephridial arrangement is the whole complex of rectum and Malpighian tubules within a membrane, i. e. having the distal ends of the Malpighian tubules closely associated with the rectum. This modification of the hindgut is exhibited by caterpillars and stored product pests (some beetles) and is concerned with improving water uptake from the rectum in the latter, and in caterpillars, it is primarily concerned with ionic regulation. Circulatory System Insects, like all other arthropods, have an open circulatory system which differs in both structure and function from the closed circulatory system found in humans and other vertebrates. In a closed system, blood is always contained within vessels (arteries, veins, capillaries, or the heart itself). In an open system, blood (usually called hemolymph) spends much of its time flowing freely within body cavities where it makes direct contact with all internal tissues and organs. The circulatory system is responsible for movement of nutrients, salts, hormones, and metabolic wastes throughout the insect's body. In addition, it plays several critical roles in defense: it seals off wounds through a clotting reaction, it encapsulates and destroys internal parasites or other invaders, and in some species, it produces (or Entomology | 87 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) sequesters) distasteful compounds that provide a degree of protection against predators. The hydraulic (liquid) properties of blood are important as well. Hydrostatic pressure generated internally by muscle contraction is used to facilitate hatching, molting, expansion of body and wings after molting, physical movements (especially in soft-bodied larvae), reproduction (e.g. insemination and oviposition), and evagination of certain types of exocrine glands. In some insects, the blood aids in thermoregulation: it can help cool the body by conducting excess heat away from active flight muscles or it can warm the body by collecting and circulating heat absorbed while basking in the sun. A dorsal vessel is the major structural component of an insect's circulatory system. This tube runs longitudinally through the thorax and abdomen, along the inside of the dorsal body wall. In most insects, it is a fragile, membranous structure that collects hemolymph in the abdomen and conducts it forward to the head. In the abdomen, the dorsal vessel is called the heart. It is divided segmentally into chambers that are separated by valves (ostia) to ensure one-way flow of hemolymph. A pair of alary muscles are attached laterally to the walls of each chamber. Peristaltic contractions of the these muscles force the hemolymph forward from chamber to chamber. During each diastolic phase (relaxation), the ostia open to allow inflow of hemolymph from the body cavity. The heart's contraction rate varies considerably from species to species -- typically in the range of 30 to 200 beats per minute. The rate tends to fall as ambient temperature drops and rise as temperature (or the insect's level of activity) increases. 88 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) In front of the heart, the dorsal vessel lacks valves or musculature. It is a simple tube (called the aorta) which continues forward to the head and empties near the brain. Hemolymph bathes the organs and muscles of the head as it emerges from the aorta, and then haphazardly percolates back over the alimentary canal and through the body until it reaches the abdomen and re-enters the heart. To facilitate circulation of hemolymph, the body cavity is divided into three compartments (called blood sinuses) by two thin sheets of muscle and/or membrane known as the dorsal and ventral diaphragms. The dorsal diaphragm is formed by alary muscles of the heart and related structures; it separates the pericardial sinus from the perivisceral sinus. The ventral diaphragm usually covers the nerve cord; it separates the perivisceral sinus from the perineural sinus. In some insects, pulsatile organs are located near the base of the wings or legs. These muscular "pumps" do not usually contract on a regular basis, but they act in conjunction with certain body movements to force hemolymph out into the extremities. About 90% of insect hemolymph is plasma: a watery fluid -- usually clear, but sometimes greenish or yellowish in color. Compared to vertebrate blood, it contains relatively high concentrations of amino acids, proteins, sugars, and inorganic ions. Overwintering insects often sequester enough ribulose, trehalose, or glycerol in the plasma to prevent it from freezing during the coldest winters. The remaining 10% of hemolymph volume is made up of various cell types (collectively known as hemocytes); they are involved in the clotting reaction, phagocytosis, and/or encapsulation of foreign bodies. The density of insect hemocytes can fluctuate from less than 25,000 to more than 100,000 per cubic millimeter, but this is significantly fewer than the 5 million red blood cells, 300,000 platelets, and 7000 white blood cells found in the same volume of human blood. With the exception of a few aquatic midges, insect hemolymph does NOT contain hemoglobin (or red blood cells). Oxygen is delivered by the tracheal system, not the circulatory system. In summary…  Open system because the body cavity houses most of the insect blood  Poorly developed in insects compared to human beings and this is somehow consistent with elaborate tracheal system and neurohemal systems; inspite of this, food distribution is efficient as well as waste product removal  Aims to bathe all tissues inside the insect body and to supply nutrients in all the cells (nothing excluded) Dorsal Vessel  Found in the pericardial sinus and is cut off by the periviscera and by the dorsal diaphragm  Made up of a single layer of muscle cells, and enclosed with connective tissues at both sides, and innervated by nerves and tracheoles to supply stimuli and oxygen Entomology | 89 AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection)   Supporting the dorsal vessel will be the alary muscles closely associated with the dorsal diaphragm, converging with the body wall and basically attached to the tergum Morphological Types of Dorsal Vessel 1. Straight Tube – mostly without segmental swellings, diverticula and other special structures (e.g. Dermaptera, Thysanura, Coleoptera, Diptera) 2. Dilatations – vessel may have series of large segmentally arranged bulbous structure (e.g. Orthoptera, Ephemeroptera, other Coleoptera) 3. Tubular Extensions – vessel may have either cephalic or post-cephalic tubular extensions; in some species may be present in abdomen (e.g. Lepidoptera, Other Diptera and Orthoptera) Note: Within the 3 major types there are special configurations; some species may have loops or kinks, or tight coils. To help in circulation, there are ACCESORY PULSATILE ORGANS. These are muscles, connective tissues, filaments or ampulla (“kulani”), located in the thorax especially the meso- and meta- thoraces or in the appendaged, and they help in blood circulation. INNERVATIONS (nerves that supply the heart) 1. Recurrent nerve on the ganglia of ventral nerve cord 2. Stomatogastric nerve system suuply heart via the occipital and ingluvial ganglionic nerves 3. Esophageal nerves The circulatory system is well innervated and thus, plays a vital role in insect survival HEMOLYMPH is the blood of insects…  it is the extracellular fluid, usually clear or colored, with green and yellow pigments coming from food  it is circulated by the heart or dorsal vessel, contains blood cells, salts, proteins, amino acids and minerals  90% of hemolymph is water  it is responsible for 16-20% of insect weight  its pH is 6 to 8.2 with specific gravity of 1.012 to 1.07  its carbon dioxide is of limited amount and in equilibrium with the bicarbonate Composition of Hemolymph (mg %) INSECTS HUMANS Total N2 1400-1700 3000-3700 Protein N2 700-900 1000-1265 Total Protein 4375-5625 6500-8200 90 |Weed Science and Other Pests AGRICULTURIST LICENSURE EXAMINATION REVIEW 2011 (Crop Protection) Non-protein N2 300-500 25-35 Free Amino Protein 200-300 5-8 Urea N2 1-10 10-15 Uric Acid 12-14 2-3.5 K 160-180 (foliage) 178 Na 20-40 (omnivorous) 178 20-60 (adult parasite) 330 Mg 10-25 1-3 P (total) 64-245 34.9 Cl 50-100 450-500 Reducing Substance (glucose) 0-25 (1000 in honeybee) 70-100 Glycogen 24 5.5 Trehalose 700-850 Glucose Lipids 398 652 Functions of the Hemolymph (Importance for insect survival) 1. transport mechanism for nutrients (digestive system), hormones (endocrine glands), waste products (dumping ground); also transport cells, blood cells, to get access of nutrients 2. storage site for water (major) and also for substances important in molting and reproduction, and serves as metabolic pool 3. hydraulic medium, thus it is important for its hydrostatic pressure (needed in molting), by controlling contractions of insect body for performance of insect function 4. thermoregulation (allows changes in hemolymph circulation patterns to increase body temperature) and frost protection 5. protection and defense against hazards Three Forms of Hazards to Insects 1. Physical Injury – like damage to integument can be helped by blood clotting which seals the wounds and facilitates repair, hence, lessening infection 2. Entry of Foreign Bodies, Compounds or Microorganisms (–this includes also insecticides) if it go through the hemolymph, there are detoxifying enzymes 3. Predation - defense by reflexive bleeding. This wards off predator How is bl