Insects: A Detailed Study PDF

**Unit I. Insects** **Definition of terms and concepts** **Entomology** - An organized body of knowledge dealing with all phases of insect life. Is the science that deals with the study of insects including their close relative, their economic importance, both beneficial and pest....

**Unit I. Insects** **Definition of terms and concepts** **Entomology** - An organized body of knowledge dealing with all phases of insect life. Is the science that deals with the study of insects including their close relative, their economic importance, both beneficial and pest. **Important things to be learned from the Science of Entomology** - Importance and relationship with plants and animals. - Insect behavior - Insect development stage - External and internal structures of insects. - Occurrences and incidences of insect pest population **Importance of Entomology** - Enhance the growth and development of beneficial organisms. - Manipulate growth and development of destructive species of insects. **Insect** - Insect if derived from the Latin word ïnsect-us" which means insecure which is to cut into. - They belong to Kingdom Animalia, Phylum Arthropoda, and Class Insecta **Insects and Plant Interrelationship** - Insect feed on plants - Insect can cause disease on plants Examples: - plant hoppers -- hopper burn - mealy bugs - wilt on pineapple - psylids - yellow disease on potato - Green Leafhoppers that transmit tungro virus on rice - Insect serves as pollinator **The Relation of Insect to Man** A. Benefits derived by man from insects 1. Pollinating services -- very essential without which \- few cereals/ vegetables/fruits 2. Provide food/source of protein for man (Insectivorous- habit of eating insects) For food -- largely cultural and attitudinal. - Mole cricket - June beetle - Winged termites - Eggs of ants - Locusts 3. Provide sources of useful products - Silk from silkworm, *Bombyx mori* - Honey/wax from bees - Lac from lac insects -- produced by scale insects *(Lacifer lacca)* which can be made into shellac or varnish 4. Organic matter decay -- The scavenger rid the earth from decaying organic matter 5. Convenient materials for scientific studies (Good indicators of water pollution) 6. Bio-control agents Predators (dragonflies, praying mantis) Parasitics (Trichogramma, Icheumonids) 7. For aesthetics/artwork 8. Effective Biocontrol agents - Parasitic -- feed only on portions of hosts - *Trichogramma spp.* - Predators -- devour/consume all the prey - Predators (beetles, bugs) 9. Effective soil aerators -- tunnelling provides oxygen 10. Bestroyer of obnoxious plants B. **Injurious Effects** 1. Injure/damage plants by feeding & ovipositing 2. Destroy man's stored products 3. Transmit diseases on man's crops \- Tomato yellow leaf curl virus by whiteflies 4. Transmit diseases on man & his animals Examples: \- *Anopheles* mosquitoes transmit malarial disease \- *Aedes* mosquito transmit dengue 5. Cause annoyance to man - creating noise - stingin - biting - emitting obnoxious odor **Historical insights in entomology** +-----------------------------------+-----------------------------------+ | **YEAR** | **DETAILED HAPPENING AS | | | REPORTED** | +===================================+===================================+ | A. **Early History** | | +-----------------------------------+-----------------------------------+ | About 3100 BC | Earliest graphic record of insect | | | (oriental hornet-wespa) found in | | | Egyptian document as kingdom | | | symbol | +-----------------------------------+-----------------------------------+ | 384 -- 322 BC | Aristotle (Father of Zoology) and | | | founder of the general entomology | | | and entomology as a science, | | | systematized knowledge in insects | +-----------------------------------+-----------------------------------+ | 23 -- 79 AD | Pliny the Elder, Roman author for | | | his 37 books published in | | | historia naturales, studied | | | insect metamorphosis | +-----------------------------------+-----------------------------------+ | 60 AD | Dioscoride, Greek military | | | surgeon described insect | | | significance to pharmacology of | | | beetle cantharidin for leprosy | | | carcinomas herpes and also dropsy | +-----------------------------------+-----------------------------------+ | 1626 - 1697 | Francisco Redi, disproved the | | | theory of spontaneous generation | | | with the aid of housefly maggot | +-----------------------------------+-----------------------------------+ | 1627 - 1705 | John Ray, wrote Historia | | | Insctorum, the first publication | | | of insect life histories | | | description | +-----------------------------------+-----------------------------------+ | 1683 - 1757 | Rene Antonie Ferchault de | | | Reaumur, initiated modern | | | entomology and produced the first | | | well illustrated classification | | | (the original) compendium of | | | entomology | +-----------------------------------+-----------------------------------+ | 1707 - 1778 | Carolus Linnaeus, father of | | | taxonomy who introduced the | | | modern system of binomial | | | nomenclature and published | | | systema naturae (classification | | | of living things) | +-----------------------------------+-----------------------------------+ | 1745 - 1808 | Johann Christian Fabricius, | | | student of Linnaeusv who | | | published systema entomologica in | | | 1775, attempted to classify | | | insect fauna of the entire world | +-----------------------------------+-----------------------------------+ | 1521 - 1899 | Spanish period, Pigafetta the | | | Italian historian made the first | | | written record of an insect in | | | the Philippines, the leaf insect | | | in Palawan in 1521 voyage of | | | Ferdinand Magellan | +-----------------------------------+-----------------------------------+ | 1593 | Spanish missionary introduced | | | silkworm rearing in the | | | Philippines | +-----------------------------------+-----------------------------------+ | 1780 | Father Galliana (Spanish | | | missionary to the Philippines) | | | re-introduced silkworm rearing | | | but did not prosper hence | | | abandoned industry | | | (laborious/unprofitable) | +-----------------------------------+-----------------------------------+ | B. **The Early American | | | Occupation (1900- 1920)** | | +-----------------------------------+-----------------------------------+ | 1902 | Charles S. Banks, an American was | | | the first Philippine government | | | entomologist who published | | | various aspects of Economic | | | Entomology, Medical entomology | | | and systematics | +-----------------------------------+-----------------------------------+ | 1904 | Charles S. Banks, published pests | | | of cacao | +-----------------------------------+-----------------------------------+ | 1908 | C.Licudan, published (first | | | extensive publication) about | | | Philippine mosquitoes | +-----------------------------------+-----------------------------------+ | 1909 | Department of entomology | | | established at UPCA UPLB Los | | | Baños headed by Edgar M. Ledyard | +-----------------------------------+-----------------------------------+ | 1910 | Bureau of Agriculture created | | | entomology section | +-----------------------------------+-----------------------------------+ | 1911 | F.O. Cevallos, presented earliest | | | works on the use of chemicals for | | | pest control in the Philippines | +-----------------------------------+-----------------------------------+ | 1912 | Second Philippine Legislative | | | ended the first quarantine law | | | Act No. 2145 | +-----------------------------------+-----------------------------------+ | 1913 | Mitzmain MS found that surra | | | disease of carabao is striated | | | transmitted by the common house | | | fly (*tabanus stratus | | | fabricius*). He was the first to | | | establish veterinary entomology | | | in the Philippines | +-----------------------------------+-----------------------------------+ | 1913 | C.H. Schultz, beekeeping using | | | imported Italian bees, first | | | attempt in the Philippines | +-----------------------------------+-----------------------------------+ | 1915 | Locust Act No. 2472 was enacted | | | by the Bureau of Agriculture on | | | locust campaign program | +-----------------------------------+-----------------------------------+ | 1915 | Leopoldo B. Uichanco, first | | | Filipino Entomology instructor, | | | MS in Entomology 1918 and PhD in | | | Entomology 1922 | +-----------------------------------+-----------------------------------+ | 1916 - 1917 | Catalogue of Philippine | | | Coleoptera by W. Schultz who | | | published this output | +-----------------------------------+-----------------------------------+ | 1919 | Plant pest section become a | | | separate division of the Bureau | | | of Agriculture | +-----------------------------------+-----------------------------------+ | C. **Onward Years of the | | | Entomology Science (1900 -- | | | 1920**) | | +-----------------------------------+-----------------------------------+ | | | +-----------------------------------+-----------------------------------+ | 1921 - 1922 | Woodworth H.E. published the | | | first comprehensive host -- index | | | of insect injurious to Philippine | | | crops | +-----------------------------------+-----------------------------------+ | 1923 | Use of soap as an effective | | | contact insecticide on the | | | control of migratory locust | +-----------------------------------+-----------------------------------+ | 1924 | Locust Scounting Act (Act 13163) | | | was passed by the Philippine | | | Legislative | +-----------------------------------+-----------------------------------+ | 1925 | First time airplane was utilized | | | for locust control | +-----------------------------------+-----------------------------------+ | 1926 | G.O. Ocfemia reported abacca | | | bunchy top virus aphids | | | transmitted (vector *Pebtalonia | | | nigronervosa*) | +-----------------------------------+-----------------------------------+ | 1927 | Use of Paris green as larvaccidae | | | for mosquitoes by Manalang | +-----------------------------------+-----------------------------------+ | 1928 - 1929 | Introduction of biocontrol agents | | | by UCPA Department of Entomology | +-----------------------------------+-----------------------------------+ | 1929 | Study on corn borer biology by C. | | | Bulligan as serious insect pest | | | of corn (*Ostrinia furnacalis*) | +-----------------------------------+-----------------------------------+ | 1931 | De Mesa, first report on forest | | | insect (wood borer) on journal -- | | | The Makiling Echo | +-----------------------------------+-----------------------------------+ | 1931 | Extensive biological studies of | | | the white grab (*Leucopholis | | | irrorata*) done separately by | | | Uichanco and Otanes | +-----------------------------------+-----------------------------------+ | 1932 | Mutation studies on the | | | Philippines wild Drosophila | | | (fruit fly) by Clemente | +-----------------------------------+-----------------------------------+ | 1933 | First study on pesticide residue | | | on vegetable crops dusted and | | | sprayed with arsemicals (J.N. | | | Samson) | +-----------------------------------+-----------------------------------+ | 1934 - 1936 | Russel and Baisas published the | | | first illustrated key to the | | | Philippine Anopheles mosquito | +-----------------------------------+-----------------------------------+ | 1934 | First report on mites of crop | | | plants in the Philippines by | | | Fajardo and Bellosillo Cendana, | | | first Filipino trained in insect | | | biological control | +-----------------------------------+-----------------------------------+ | 1939 | DDT | | | (Dichloro-Diphenyl-Trichloroethan | | | e) | | | by Paul Herman Muller, a Swiss | | | chemist | +-----------------------------------+-----------------------------------+ | 1941 | Viado, first insecticide | | | toxicologist in the Philippines | +-----------------------------------+-----------------------------------+ | 1946 | DDT introduction in the | | | Philippines for house fly and | | | migratory locust | +-----------------------------------+-----------------------------------+ | 1947 | Cendana and Baltazar reported | | | cotton leafhopper (*Empoasca | | | bigutullla*). Claire R. Baltazar | | | was the first Filipina | | | entomologist (B.S. Entomology ) | | | after World War II | +-----------------------------------+-----------------------------------+ | 1954 | First studies conducted on plant | | | resistance to insect by S.M. | | | Cendana using corn hybrid and | | | inbred on corn borer | +-----------------------------------+-----------------------------------+ | 1959 | Introduction of IPM concepts (ETL | | | and EIL) | +-----------------------------------+-----------------------------------+ | 1960 | Entomology researches in the | | | Philippines were further boosted | | | especially on rice insect pest | | | with the establishment of IRRI at | | | Los Baños within UPCA | +-----------------------------------+-----------------------------------+ | 1961 | Leo C. Rimando, first Filipino | | | Acarologist (Mite Specialist) | +-----------------------------------+-----------------------------------+ | 1962 | July 22, 1962, Philippine | | | Entomological Socirty (PES) now | | | Philippine Association of | | | Entomologist Incorporated was | | | organized. S.M. Cendana was the | | | first President | +-----------------------------------+-----------------------------------+ | 1962 | Rachel Carlson's Silent Spring | | | (birds mortality due to DDT) | +-----------------------------------+-----------------------------------+ | 1962 | Venus Calilung, Filipina | | | Aphidologist (Aphid virus) | +-----------------------------------+-----------------------------------+ | 1962 | Thaddeus W. Harris, founder of | | | applied entomology in the USA | +-----------------------------------+-----------------------------------+ | 1962 | Ferino, who discussed/identified | | | rice whorl maggot (as the | | | taxonomist the species) | +-----------------------------------+-----------------------------------+ | 1964 | B.P. Gabriel, first Filipino | | | insect pathologist. IRRI | | | international symposium on rice | | | insect pest | +-----------------------------------+-----------------------------------+ | 1966 | Publication of Philippine | | | Hymenoptera catalogue by C.R. | | | Baltazar- the first catalogue | | | done by Filipino | +-----------------------------------+-----------------------------------+ | 1967 | First national meeting of PAE | | | held at UPCA in August 12, 1967 | +-----------------------------------+-----------------------------------+ | 1972 | Banning of DDT in the USA | +-----------------------------------+-----------------------------------+ | 1976 | Founding of national crop | | | protection in May 19, 1976 at | | | UPLB | +-----------------------------------+-----------------------------------+ | 1978 | First regional meeting of PAE in | | | Davao City (February 17. 1978) | +-----------------------------------+-----------------------------------+ **Recognizing an insect from other arthropods** **Phylum Arthropoda** - Derive from the two Greek words Arthron which means joint and Pous meaning foot. - Organisms that is jointed legs. **Distinguishing characteristics of phylum Arthropoda** - Bilaterally symmetrical ​ - Horizontally oriented​ - Forwardly progressing​ - Body divided by groves to form segments​ - Well-developed body covering (integument) which makes up the outer shell (exoskeleton) ​ - Body segments have 1 or more jointed appendages​ - Heart is dorsal; nerve cord is ventral ​ **Classes of organisms under phylum Arthropoda** 1. **Class Arachnida** - Mouthparts are called chelicerae - Most contain venom - Antennae are absent - Four pairs of legs - Book lungs for respiration - Spiders, mites, ticks, scorpions 2. **Class Crustacea** - They have two main body division the head and cephalothorax - They have five to seven pairs of legs - They have two pairs of antennae - They have only simple eyes - Examples are crabs, lobster, sowbugs. 3. **Class Chilopoda** - They have one pair of legs per body segments - They have flattened body - The first pair of their legs is modified as venomous fangs - They are nocturnal predators - Few are dangerous to human - They have 16 pairs of legs - Centipede 4. **Class Diplopoda** - They have two pairs of legs per body segment - They have cylindrical body - Feed on decaying plant material - They are nocturnal and harmless - Milipede 5. **Class Insecta** - They have three body divisions namely head, thorax, and the abdomen - They have a pair of antennae - They have compound eyes - They have 3 pairs of legs - They have one to two pair of wings **Aspects of Class Insecta** Characteristics of insects - Three tagmata: head, thorax and abdomen​ - A pair of antennae​ - Compound eyes​ - Three pairs of legs​ - One to two pair of wings​ Significance of insects - They are the dominant group of animals in our planet - Are the most numerous - Very adaptive - Have lived about 350 million (human 2 million) - Great importance for the balance for global ecosystem - Pollinate a vast majority of world's species of flowering plants - Insects recycle nutrients - Insects are small in size - Some very valuable to human. Honey; bees - silk; silkworm - dyes; aphids Food; locust, dragonflies, larvae. Beneficial insects controlling potential pest - Some are very harmful to human - Carrier of diseases (viruses, bacteria, and fungi) - Responsible for innumerable animal and human diseases (malaria, dengue, typhus) - Poisonous -- sting allergies - Causing losses in agricultural crops Physiology and behavior of insects - Cold blooded animals, body temperatures follow closely the outside temperature, can withstand adverse climatic condition. - Reproductive powers of insects can be tremendous, depend on the numbers of eggs laid by the female insects. - Complex and fascinating social behavior. - Defense mechanism against enemies. Inventions of insects - Creating nets to capture prey - Hornets makes paper - Insects are constructing elaborate buildings - Some insects have cold light and chemical warfare - Solve problems of aerodynamic and celestial navigation - Many insects have elaborate navigation systems involving chemicals **Characteristics as a group** 1. Body architecture is unique - Exoskeleton (outer shell) -- light yet strong and protective - Appendages -- adapted for specific purpose mouth - feeding legs & wings - locomotion 2. Small size -- size range from 2mm -3cm - Facilitates dispersal - Facilitates easy escape from natural enemies - Enables them to use food in small amounts 3. Ability to fly -- having wings help them to: - Disperse widely - Colonized new habitat - Escape from enemies - Evolve new species 4. High reproductive powers -- produce offspring\'s ranging from several hundreds to thousands which allows them to persist with higher variability. 5. Short life cycle - Some insects complete their cycle in 10-15 days (Black bean aphid) 6. Strong sense of smell - Could find food/ mates at distant places 7. Strong sense of vision - Compound eyes -- made up of small lenses with visual range of 20-30 degrees 8. Unique defense mechanism - Spiky/hairy bodies - Stings to paralyzed enemies - Warning coloration - Chemical warfare - Camouflage **Recognizing an insect from other arthropods** **Phylum Arthropoda** - Derive from the two Greek words Arthron which means joint and Pous meaning foot. - Organisms that is jointed legs. **Distinguishing characteristics of phylum Arthropoda** - Bilaterally symmetrical ​ - Horizontally oriented​ - Forwardly progressing​ - Body divided by groves to form segments​ - Well-developed body covering (integument) which makes up the outer shell (exoskeleton) ​ - Body segments have 1 or more jointed appendages​ - Heart is dorsal; nerve cord is ventral ​ **Classes of organisms under phylum Arthropoda** 6. **Class Arachnida** - Mouthparts are called chelicerae - Most contain venom - Antennae are absent - Four pairs of legs - Book lungs for respiration - Spiders, mites, ticks, scorpions 7. **Class Crustacea** - They have two main body division the head and cephalothorax - They have five to seven pairs of legs - They have two pairs of antennae - They have only simple eyes - Examples are crabs, lobster, sowbugs. 8. **Class Chilopoda** - They have one pair of legs per body segments - They have flattened body - The first pair of their legs is modified as venomous fangs - They are nocturnal predators - Few are dangerous to human - They have 16 pairs of legs - Centipede 9. **Class Diplopoda** - They have two pairs of legs per body segment - They have cylindrical body - Feed on decaying plant material - They are nocturnal and harmless - Milipede 10. **Class Insecta** - They have three body divisions namely head, thorax, and the abdomen - They have a pair of antennae - They have compound eyes - They have 3 pairs of legs - They have one to two pair of wings **Aspects of Class Insecta** Characteristics of insects - Three tagmata: head, thorax and abdomen​ - A pair of antennae​ - Compound eyes​ - Three pairs of legs​ - One to two pair of wings​ Significance of insects - They are the dominant group of animals in our planet - Are the most numerous - Very adaptive - Have lived about 350 million (human 2 million) - Great importance for the balance for global ecosystem - Pollinate a vast majority of world's species of flowering plants - Insects recycle nutrients - Insects are small in size - Some very valuable to human. Honey; bees - silk; silkworm - dyes; aphids Food; locust, dragonflies, larvae. Beneficial insects controlling potential pest - Some are very harmful to human - Carrier of diseases (viruses, bacteria, and fungi) - Responsible for innumerable animal and human diseases (malaria, dengue, typhus) - Poisonous -- sting allergies - Causing losses in agricultural crops Physiology and behavior of insects - Cold blooded animals, body temperatures follow closely the outside temperature, can withstand adverse climatic condition. - Reproductive powers of insects can be tremendous, depend on the numbers of eggs laid by the female insects. - Complex and fascinating social behavior. - Defense mechanism against enemies. Inventions of insects - Creating nets to capture prey - Hornets makes paper - Insects are constructing elaborate buildings - Some insects have cold light and chemical warfare - Solve problems of aerodynamic and celestial navigation - Many insects have elaborate navigation systems involving chemicals - Pheromones; fruit flies - Sounds; cicadas and beetles - behavior; honeybee dance - Light; fireflies **Characteristics as a group** 3. Body architecture is unique - Exoskeleton (outer shell) -- light yet strong and protective - Appendages -- adapted for specific purpose - mouth -- feeding - legs & wings - locomotion 4. Small size -- size range from 2mm -3cm - Facilitates dispersal - Facilitates easy escape from natural enemies - Enables them to use food in small amounts 7. Ability to fly -- having wings help them to: - Disperse widely - Colonized new habitat - Escape from enemies - Evolve new species 8. High reproductive powers -- produce offspring\'s ranging from several hundreds to thousands which allows them to persist with higher variability. 9. Short life cycle - Some insects complete their cycle in 10-15 days (Black bean aphid) 10. Strong sense of smell - Could find food/ mates at distant places 9. Strong sense of vision - Compound eyes -- made up of small lenses with visual range of 20-30 degrees 10. Unique defense mechanism - Spiky/hairy bodies - Stings to paralyzed enemies - Warning coloration - Chemical warfare - camouflage **Unit II. Entomology** **Internal Structure of Insect** General Structure of an Insect Insects are elongated, cylindrical and bilaterally symmetrical invertebrates. The body is divided into three regions: the head, thorax and abdomen (Figure 1). 1. The head bears the compound eyes and usually three simple eyes, distributed in a triangular fashion in the vertex or forehead; the antenna and mouthparts. These structures are used for sensation and ingestion. 2. The next body region, the thorax is composed of three segments, (prothorax, mesothorax and metathorax), each pair bearing a pair of legs, with the second and third segments each bearing a pair of wings. The plate bearing the wings is called pterothorax. The thorax is the locomotor segment of the insect. 3. The posterior region of the body is the abdomen, consisting of as many as 11 segments and has no legs. The eighth, ninth and tenth segments usually have appendages modified for mating activities or egg-laying. A diagram of a grasshopper Description automatically generated Figure 1. The principal body regions and components of the typical insect. **The body wall (Exoskeleton)** Insects possess an external covering called integument or exoskeleton. It is made up of chitin, a protein which makes it water proof, flexible, sturdy, and resistant to chemicals. The external layer of the skeleton is covered by a waxen layer called cuticle that is highly impenetrable to water. In some insects, the exoskeleton is tanned and hardened due to the deposition of sclerotin. This provides sturdiness and water resistance while chitin provides mobility. Functions of exoskeleton 1. serves as the insect's skeleton 2. provides support and shape to the insect body 3. protecting its vital internal organs 4. serves as a framework for muscle attachment 5. provides control in movement. Main sclerites or areas of the head There are more or less well-defined plates or regions or sclerites on the surface of the head which are partitioned by shallow grooves called sutures (Figure 2). 1. Vertex: Sclerite located on top of the head capsule (dorsal surface) above the frons between the compound eyes 2. 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. 3. Frons: Triangular sclerite that lies between these frontal sutures; the anterior sclerite of the head. 4. Epistomal suture is a deep groove that separates the base of the frons from the clypeus. 5. Clypeus is a transverse sclerite on the lower front margin of the head capsule below the frons. 6. Genae (\"cheeks\"): Lateral sclerites lying behind the frontal sutures on each side of the head 7. Occiput: Horsecollar-shaped sclerite is located at the back of the head. **The Insect Head** - Usually a solid capsule (epicranium) without obvious segmentation due to the complete fusion of 6 or 7 primitive segments - Specialized for food gathering and manipulation, sensory perception and neural integration - Head capsule consists of: Vertex-dorsal aspect; Gena-cheek, lateral aspect; Frons-anterior aspect; clypeus-lip-like sclerite; Occiput, posterior aspect which connects to the thorax; the mouthparts at the bottom or ventral aspect. - The head bears the eyes, a pair of antennae and the mouthparts.  Figure 2. The common lines or grooves on the insect head and the areas which they define. Names of areas are italicized. (Adapted from Snodgrass,1960) Orientation of the insect head The orientation of the head with respect to the rest of the body is variable (Figure 3). These types of head directions are adaptations to their different environments or manner of feeding. 1. Hypognathous head: the most primitive condition, with the head in vertical position and the mouthparts directed ventrad or downward, e.g. grasshopper. 2. Prognathous head: in a horizontal orientation and the jaws are directed forward. The cranium is turned upward on the neck so that the mouthparts are directed forward, e.g. carnivorous insect, carabid beetles (actively hunt their prey). 3. Opisthognathous/opisthorrynchous head: with a posterior ventral position of the mouthparts with a deflection of the facial region. Hence, the head is directed towards the abdomen. The elongate proboscis slopes backward between the front legs, e.g. cicada, all members of the orders: Homoptera/Heteroptera. Eyes - Insects have two kinds of eyes: the compound eyes and the simple eyes or ocelli (singular, ocellus). The ocelli are very well adapted to observe movement as well as distinguishing between forms and colors. - Insect distinguish blue and yellow colors more easily while red color cannot be seen. Hence, - blue and white are light are used in light traps - The ocelli appear to enhance light detection by the compound eyes and to record cyclical changes in light intensity that is connected with diurnal behavioral rhythms. Compound eyes - Located on each side of the head, consist of many hexagonal elements called facets or corneal lenses. - The number of facets in a compound eye varies from only a few in the springtails to as many as 28,000 as in the dragonflies. - Faceted: Each lens consists of sensory cells representing the outer portion of a single eye element or ommatidium - Large and occupy part of the vertex, frons, gena and occiput Simple eyes (Ocelli) - Three ocelli, commonly arranged in triangular fashion on the vertex between the compound eyes - Each lateral (or posterior) ocellus has a single lens, that can perceive light but cannot form images. It provides clues about intensity of light and influence their level of activity. - 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 whole vision is influenced by simultaneous performance of all ommatidia in which the image is recognized. If some of these facets are injured, the object as viewed by the insect will have lacking pieces consistent to the loss of image due to the nonfunctional lenses. Antennae The antennae are a pair of segmented appendages on the head located usually between or below the compound eyes. The antennae are sensory in function, such as: 1. acting as tactile organs, 2. organs of smell (with olfactory receptors that detect odor molecules in the air) 3. humidity receptors (detect changes in concentration of water vapor) 4. organs of hearing (mosquitoes detect sounds) 5. gauge air speed during flight (flies) The antennae are divided into three basic parts, namely: 1. Scape - basal segment that articulates with the head capsule; contains intrinsic muscles and is generally larger than the other segments. 2. Pedicel - second antennal segment; nearly always contain a sensory organ called Johnston's organ 3. Flagellum or clavola - remaining segments which respond to the movement of the distal part of the antennae relative to the pedicel The insect antennae vary greatly in size and shape and are much used in classification. 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 (Adapted from Borror, DeLong and Triplehorn, 1976 +-----------------------+-----------------------+-----------------------+ | **Name/Description** | **Appearance** | **Example(s)** | +=======================+=======================+=======================+ | Setaceous (bristle- |  -- segments | ) | | | becoming more slender | | | | dorsally | | | +-----------------------+-----------------------+-----------------------+ | Filiform | | Grasshoppers and | | (thread-like) - | | Cockroaches | | segments nearly | | | | uniform in size, | | | | usually cylindrical | | | +-----------------------+-----------------------+-----------------------+ | Moniliform |  - | ) | | | segments similar in | | | | size, more or less | | | | cylindrical | | | +-----------------------+-----------------------+-----------------------+ | Serrate (saw-toothed) | | Female giant click | | - segments | | beetle | | particularly the | | | | distal half, more or | | | | less triangular | | | +-----------------------+-----------------------+-----------------------+ | Clavate (gradually |  - segments | g) | beetles | | gradually increase in | | | | size distally | | | +-----------------------+-----------------------+-----------------------+ | Capitate (abruptly | | Skin beetles | | clubbed) -- terminal | | | | segments are rather | | | | suddenly enlarged | | | +-----------------------+-----------------------+-----------------------+ | Lamellate -- the |  | | | expanded laterally to | | | | form rounded or oval | | | | plate-like lobes | | | +-----------------------+-----------------------+-----------------------+ | Flabellate -- | | Cedar beetle | | terminal segments | | | | with long, | | | | parallel-sided, | | | | sheet-like or | | | | tongue-like lobes | | | | extending laterally | | | +-----------------------+-----------------------+-----------------------+ | Pectinate (comb-like) |  | Male glow-worms and | | long, slender lateral | | Male giant click | | processes | | beetles | +-----------------------+-----------------------+-----------------------+ | Plumose (brush-like | | Male mosquitoes | | or feathery) - | | | | segments with whorls | | | | of long hairs | | | +-----------------------+-----------------------+-----------------------+ | Bipectinate (double |  -- all | g) | silkworm moth | | segments of both | | | | sides of the antenna | | | | are with long lateral | | | | processes) | | | +-----------------------+-----------------------+-----------------------+ | Geniculate (elbowed) | | Weevils and Ants | | - first | | | | | | | | segment long, | | | | following segments | | | | | | | | small and going off | | | | at an angle to | | | | | | | | the first | | | +-----------------------+-----------------------+-----------------------+ | Aristate (pouch-like |  | flies | | bristle) - last | | | | segment usually | | | | enlarged and bearing | | | | a conspicuous arista | | | +-----------------------+-----------------------+-----------------------+ | Stylate the last | | Robber fly | | segment bearing an | | | | elongate terminal | | | | finger-like process | | | | called style | | | +-----------------------+-----------------------+-----------------------+ Mouthparts Mouthparts of insects are one of the most distinguishing characteristics of insect species which suggest their feeding habits. In all insects, the mouthparts have evolved from a basic or primitive type (chewing type) as demonstrated by the grasshopper. The insect generalized (chewing) mouthparts consists of component parts surrounding a mouth opening or oral cavity. These include: a labrum (upper lip), a pair of chewing mandibles (jaws), a pair of maxillae (second jaws), and a labium (lower lip). 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 is based on the mouthparts that are adapted for biting and chewing. **Labrum:** movable plate attached to the lower margin of the clypeus with its outer surface generally strongly sclerotized and its distal margin sharply defined. **Epipharynx:** interior or ventral surface of the labrum, membranous with tactile hairs and taste organs. **Mandibles:** a pair of strongly sclerotized, unsegmented jaws located immediately posterior to the labrum. 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. **Maxillae:** paired segmented structures, lying posteroventral to the mandibles and antero-dorsal to the labium. The basal segment, the cardo, is attached to the head proximally and to a longer 2ndsegment, the stipes, distally. The stipes bear two lobes, the lateral galea and the mesal lacinia. Attached laterally to the distal part of the stipes are the usually 1--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 accessory 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. **Labium:** consists of the fused 2nd 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 paraglossalaterally; and a pair of 1 -- 4 segmented labial palps arising from a lateral part of the prementum which is sometimes differentiated as the palpiger. When the prementum is divided transversely into 2 parts, the distal portion bearing the glossae and paraglossae is known as the ligula. **Hypopharynx**: 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. As a modification of the chewing type of mouthparts, insects have types that include piercing-sucking, rasping-sucking, siphoning, sponging and chewing lapping. The type of mouthparts of an insect defines its feeding routine and the type of damage it inflicts on its host. 1. Piercing-sucking mouthparts - 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-hair-like 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 serves 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-epipharynx which forms a food channel. The stylets are enclosed by a protective sheath formed from an elongated labium. The back of thefood channel is closed by the hypopharynx with its salivary duct carrying saliva which contains enzymes and anticoagulants that reduce blood clotting in the host and improveand improve the flow of blood into the mosquito. The maxillary and mandibular stylets work together as a needle to penetrate the host skin. 2. Rasping-sucking mouthparts - Characterized as a short, stout, assymetrical conical structure located ventrally at the rear of the head - Primitive form of the piercing-sucking type, found in thrips (Thysanoptera) - 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. 3. Siphoning mouthparts - Highly specialized type, modified for the uptake of flower nectar and other liquids - Found in practically all adult moths and butterflies (Lepidoptera) - The galea of the maxillae are greatly elongated and joined to form a slender hollow tube called proboscis through which food passes and held in coiled-spring fashionwhen 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 lengththrough the proboscis. 4. Sponging mouthparts - Highly specialized structures found in common housefly - 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 the food is not liquid, salivary secretions through the mouthparts make it so. 5. Chewing -lapping mouthparts - Found 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 are 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. - Found in bees and wasps (Hymenoptera) **The Insect Thorax** - The second (middle) tagma of an insect\'s body; body region between head & abdomen - Almost exclusively adapted for locomotion \-- contains three pairs of walking legs and, in many adult insects, one or two pairs of wings; Main engine room of the insect; Legs and wings are attached. - Made up of a series of concave (upper) and convex (lower) integumental plates (Nota/notum) and the whole being held together by a tough yet stretchable membrane (Pleura/pleuron) - Composed of 3 segments, prothorax, mesothorax, metathorax; the fore-legs are located on the prothorax, mid-legs and the forewings on the mesothorax, hind legs and hind wings on the metathorax. - Each thoracic segment consists of the following: - Tergum---notum (located dorsally) - Sternum- ventral plate joined by anterior and posterior bands of the pleura (located ventrally) - Pleuron---sclerite which become enlarged to form a lateral plate; two sclerites: an anterior episternum and a posterior epimeron Insect Legs 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. Typically, the legs of insects are sclerotized and divided into six segments. 1. Coxa- most basal aspect of the insect leg and articulates with the sternites; 2. Trochanter-usually small and serves as a joint between the coxa and the femur; 3. Femur- usually long and stouter than the other segments and contains the main muscles used in running, jumping and digging; 4. Tibia---generally long serving to increase the length of the leg, as well as adding an extra joint and thus extra flexibility the underside of the tarsal segments may possess pads; 5. Tarsus- series of small subdivisions beyond the tibia; and 6. Pretarsus -- consists of claws and pad-like or seta-like structure at the apex Between the claws may be found a special pad known as arolium which acts using suction developed by large numbers of minute tubular hairs to help hold the insect to smooth substrate. The term pretarsus refers to the terminal segment of the tarsus and any other structures attached to it, including: 1. ungues -a pair of claws 2. arolium -- a lobe or adhesive pad between the claws 3. empodium -a large bristle (or lobe) between the claws 4. 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. These leg adaptations and modifications made them more adapted to their environments. **Leg Modifications and Adaptations** 1. Ambulatorial - Walking/ running - Cockroach 2. Saltatorial - Jumping - Grasshoppers with enlarged femur 3. Raptorial - Grasping - Praying mantis with sharp opposing spurs and spines 4. Natatorial - Swimming - Diving beetle with long brushes of hair and flattened parts 5. Fossorial - Digging - Mole cricket with strong scraper-like parts 6. Clasping - Lice with well-developed claws on the prothoracic leg 7. Assembling - Pollen-gathering hind tibiae with hairs (pollen basket or corbicula) - Well-developed and hairy pollen basket of honeybees where the pollen adhere to **Insect Wings** The wings are lateral outgrowths of the body wall attached dorso-ventrally in the mesothorax and metathorax. A typical insect wing is membranous with sclerotized veins for flight. It consists of double layer of extremely thin cuticle which interspersed with hollow veins filled with either air or blood. Insects are the only invertebrates that can fly. Their wings develop as evaginations of the exoskeleton during morphogenesis but they become fully functional only upon adulthood. Wing venation is commonly-used as taxonomic character, especially at the family and species level. Adult insects have one or two pairs of wings; some have none. Insects have evolved many variations of the wing. Wing shape, texture, and venation are quite distinctive among the insect taxa and are highly useful as aides for identification. The veins of the wings 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. Wings serve not only as organs of flight, but also may be adapted variously as: 1. protective covers (Coleoptera and Dermaptera) 2. thermal collectors (Lepidoptera) 3. gyroscopic stabilizers (Diptera) 4. sound producers (Orthoptera) 5. visual cues for species recognition and sexual contact (Lepidoptera) Types of insect wings 1. Elytra: Hard, sclerotized front wings that serve as protective covers for membranous hind wings (beetles: Coleoptera) 2. Hemelytra: Front wings leathery or parchment-like at the base and membranous near the tip (true bugs: Hemiptera) 3. Tegmina: Front wings are completely leathery or parchment-like in texture (grasshoppers: Orthoptera) 4. Haltere: Small, club-like hind wings that serve as gyroscopic stabilizers during flight (true flies: Diptera) 5. Fringed wings: Slender front and hind wings with long fringes of hair (thrips: Thysanoptera) 6. Hairy wings: Front and hind wings clothed with setae (caddisflies: Trichoptera) 7. Scaly wings: Front and hind wings covered with flattened setae (scales) (butterflies and moths: Lepidoptera) 8. Membranous The veins of the wings are obviously apparent (Hymenoptera and Odonata) Wing adaptation 1. Wing coupling: insects that have two pairs of wings have special devices to keep the wings coupled during flight 2. Hamuli: Tiny hooks on hind wing that fold front and hind wings together (Hymenopterans) 3. Frenulum: Bristle near base of hind wing that holds front and hind wings together (Lepidopterans) 4. Jugum: Lobe-like process at the base of the forewing which overlaps the hindwing. The coastal margin of the hindwing fits into a projecting jugum holding the hindwing in place during flight. **Insect Abdomen and its Appendages** The insect abdomen - Third and posterior region of insect body - Consist of 10 or 11 segments but is reduced in some forms - Typical segments in adults consists of tergum (dorsal plate); sternum (ventral plate), lateral areas of membrane connecting tergum and sternum and a spiracle on each side. - The anus (rear opening to the alimentary canal) is located at the end of the abdomen, snuggled between 3 protective the dorsal periproct and 2 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. **Function of the abdomen** - Concerned with digestion - In reproduction - As defense Distinct regions of the abdomen Reproductive appendages The insect\'s genital opening lies just below the anus. The genital opening is surrounded by specialized sclerites that form the external genitalia. - In females, paired appendages of the eighth and ninth abdominal segments fit together to form an egg-laying mechanism called the ovipositor. Structural differences in the copulatory organs furnish excellent taxonomic characters in insects for the differentiation of families, genera or species - In males, the appendages of the 9th segment are usually combined with parts of the 10th to form a copulatory organ. - 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 such as the subgenital plate, claspers, and styli 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. Abdominal appendages of insects 1. Pincers (cerci): Heavily sclerotized and forcep-like; used for defense (Earwigs) 2. Median caudal filament: Head-like projection arising from the center of the last abdominal segment (between cerci); (Diplura, Thysanura, Ephemeroptera) 3. 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. 4. Abdominal prolegs: Fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera). 5. Sting: Modified ovipositor, found only in the females of Hymenoptera (ants, bees, and predatory wasps). 6. Abdominal gills: Respiratory organs found in the nymphs (naiads) of certain aquatic insects (Ephemeroptera) 7. Furcula: The \"springtail\" jumping organ found in Collembola on the ventral side of the fifth abdominal segment. 8. Collophore 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 **Unit III. External Structure of Insects** **Digestive System** **The digestive tract aids in obtaining, processing and digesting food molecules** **The digestive system is involved in:** 1. **Obtaining food** 2. **Mechanically breaking it down into smaller particles that facilitate digestive enzymes acting on them** 3. **Enzymatic breakdown of larger food molecules into molecules that can pass through the digestive tract (midgut) and enter the hemolymph** 4. **Produces molecules or MESSENGERS (eg. Endocrines), that coordinate feeding and other activities of the digestive tract** **Parts of the digestive tract (Figure 1):** 1. **Foregut/Stomedeum -- food is stored, filtered and partially digest** 2. **Midgut/Mesenteron/Ventriculus -- primary site of digestion and absorption of food** 3. **Hindgut/Protodeum -- some absorption and feces formation occur**  **https://bugwoodcloud.org/bugwoodwiki/Digestive\_system.jpg** ***Figure 2. The different parts of the digestive tract.*** 1. **[FOREGUT]** - **Starts from mouth cavity to gizzard or proventriculus** - **The mouth cavity: labrum as the upper lip, labium as the lower lip with mandibles and maxillae laterally and hypopharynx at the center.** - **At the base of the of the hypopharynx, salivary glands open into the mouth cavity.** - **Salivary glands -** the glands are grape-like cluster called acinus, involved in the secretion of salivary juices and into the salivary ducts - **Functions of saliva** - **To moisten and to dissolve food** - **To lubricate mouthparts** - **To add flavour to gustatory receptors** - Divided into: - Pharynx -- region between the mouth and oesophagous - Oesophagous -- it is narrow part, food get transported from pharynx into the crop - Crop -- it is a sac like structure which is a dilated and store food material - Gizzard/Proventriculus -- a structure that contain sclerotized teeth-like denticles. These denticles grind the food (lack in fluid feeding insects) - The junction of foregut and midgut is provided with a cardiac (oesophageal) valve also called stomodeal valve (regulate the flow of food) - The foregut is lined with chitinous protective layer called intima. Intima prohibits the absorption of nutrients 2. **[MIDGUT]** - **A short, cylindrical and straight tube** - The posterior end of the midgut is marked by the presence of malphigian tubules which absorbed nutrients - At the junction of midgut and hindgut is a pyloric valve - The midgut has a very thin and delicate layer called peritrophic membrane secreted by the epithelial cells - The peritrophic membrane protects the tender epithelial cells/secretary cells of the midgut from friction by hard food particles. It forms a coat over the food particles - The midgut is not line by intima and most of absorption of nutrients occurs here 3. **[HINDGUT]** - **Malpighian tubules are attached to pylorus region of hindgut** - **Divide into:** - Ileum (small intestine) -- is a thick and straight tube - Colon (large intestine) -- is a short and narrow tube which dilates posteriorly to merge into the rectum - Rectum -- wider tube provided with six bands of longitudinal muscles alternating. These are involved in the reabsorption of water and salts from the faecal matter. - Major refuse dumping area for waste products from midgut and malpighian tubules - **Involved in getting rid of excessive water and also in housing symbionts that use these waste products to produce substances the insect needs.** - Special adaptations of the hindgut region that aid in reabsorption of certain salts and amino acids. Helps in maintaining osmotic pressure of the hemolymph - Water absorption from feces into the hemolymph *Figure 3. Part of the digestive tract.* **Organs for excretion** 1. Malpighian tubules - Thin, blind-ending originating near the junction of mid and hindgut - Predominantly involved in regulation of salt, water and nitrogenous waste excretion - Discovered by Marcello Maipighi 2. Nephocytes -- cells that sieve the hemolymph for products that they metabolize 3. Fat bodies- loose or compact aggregation of cells mostly tropocytes suspended in the haemoceal, responsible for storage and secretion 4. Integument -- the outer covering of the living tissues of insects 5. Tracheal system- allows gas the water to enter and leave 6. Rectum -- the posterior part of hindgut **Insect Circulatory System** - **Responsible in the movement of nutrients, salts, hormones and metabolic wastes** - **Play role as defense** - **It seals off wounds through clotting reaction** - **It encapsulates and destroys internal parasites and other invaders** - **In some species, it produces distasteful compounds that provide a degree of against predators** **Insect Circulatory Organs** 1. **Dorsal vessel** - 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. - it is further divided and often constricted into 5 to 6 heart chambers separated by valves (ostia) to ensure unidirectional flow of hemolymph. 2. Heart - 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 3. Alary muscle - attached laterally to the walls of each chamber - Alary muscles are 2 thoracic and 10 abdominal in grasshoppers and 4-7 pairs in bugs. - Peristaltic contractions of these muscles force the hemolymph forward from chamber to chamber. 4. Aorta - It is a simple tube 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. 5. **Ostia** - During each diastolic phase/relaxation, the ostia open to allow inflow of hemolymph from the body cavity and during contraction of heart these ostia closes and the hemolymph move forward. 6. Pulsatile organ - in some insects, these 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 **Respiratory system** **Respiration** - **Includes both the process by which gaseous oxygen is introduced into the insect** - **Process by which oxygen is combined with the substrates to produce energy** - **Oxygen comes from the atmosphere regardless of the habitat and it always crosses the membranes to reach the cells in the animal where it is utilized in aqueous solution** - **Carbon dioxide is produced as end product of the metabolic activity and is eventually liberated at least in part in a gaseous state** - **In insect some of the gaseous product is converted to carbonate and excreted as such** **Structure of the Respiratory System**  * * **Respiratory Organs** 1. Spiracles - opening is controlled by sphincters - it opens when the insects are active to allow oxygen to come into the tracheal system - it will be close when they are at rest to prevent the loss of excess water 2. Trachea - The spiracles lead to the longitudinal tube called trachea lined with intima propria. - Main tube where the air goes through the body - No gas exchange is happening because of the chitin 3. Tracheoles - The longitudinal tracheal trunk gives a complex, branching network of tracheal tubes that subdivides into smaller and smaller diameters and reaches every part of the body called tracheoles. - Tracheoles are enclosed in a very thin layer of cytoplasm from the tracheal end cell (tracheoblast). - No chitin, there is gas exchange - Surrounded with tracheal fluids which limits air penetration 4. Air sac - In some areas, however, there are no taenidia, and the tube swell like a balloon to form air sac capable of storing/reserve air. - Air sacs are mostly the characteristic feature of flying insect as taenidia absent. It increases the volume of air which performs various functions prevent collapsing, heat conservation, forms tympanic cavity aid in hearing organ in Cicada moth.  *https://insectsdiditfirst.com/2013/06/24/going-micro-tubular/* Nervous system - A network of specialized cells called neurons that serve as an "information highway" within the body - The nerve cell or neuron composed of a cell body with two projections (fibers) - Dendrites -- receives stimuli - Axon - Transmits information either to another neuron or to an effector organ such as muscle - May have lateral branches called collateral and terminal arborisation and synapse C:\\Users\\Michael\\Desktop\\Marz Files\\Insect Physiology\\Pics Chap 8\\Capture 3.PNG *https://faculty.ksu.edu.sa/sites/default/files/insect\_nervous\_system\_1.pdf* - Anatomically the insect nervous system is divide into: - Central nervous system (CNS) - Brain - It is the dorsal ganglion center of the head. It is lying above the anterior end of stomodeum. Subdivide into three main regions: - Protocerebrum -- associated with the eyes and thus bearing the optic lobes - Deutocerebrum -- innervating the antennae - Tritocerebrum -- concerned with handling the signals that arrive from the body. Main sensory centre in controlling insect behaviour - Suboesophageal ganglia -- formed by the last three cephalic neuromeres which innervate mandible, maxillae and labium - Ventral nerve cord - Thoracic ganglia -- three pairs found in the respective thoracic segments largest ganglia innervate legs and muscle - Abdominal ganglia -- median chain of segmental ganglia beneath oesopahagus Insect nervous system - Visceral/Sympathetic nervous system (SNS) -- consist of three separate systems - Stomodeal/stomatogastric -- frontal ganglion and connected with aorta, foregut and midgut - Ventral visceral -- associated with ventral nerve cord - Caudal visceral -- associated with the posterior segments of abdomen and reproductive organ - Peripheral nervous system - Sensory neurons of the cuticular sensory structures that receive mechanical, chemical, thermal or visual stimuli from an environment. All the motor neuron axons that radiate to the muscles from the ganglia of the CNS and visceral nervous system **Reproductive system** - Insects have a high reproductive rate and a short generation time. They evolve faster and can adapt to environmental changes much faster than other slower breeding animals - Reproductive system is meant for mating and reproduces young ones Male reproductive system - The main functions of the male reproductive system are the production and storage of spermatozoa and their transport in a viable state to the reproductive tract of the female. - Morphologically, the male tract consists of paired testes, each containing a series of testicular tubes or follicles (in which spermatozoa are produced) which open separately into the mesodermally derived sperm duct or Vas deferens which expands posteriorly to form a sperm storage organ or seminal vesicle. Tubular paired accessory glands are formed as diverticula of the vasa deferentia. Sometimes the vasa deferentia themselves are glandular and fulfil the functions of accessory glands. The paired vasa deferentia unite where they lead into the ectodermally derived ejaculatory duct (the tube that transports the semen or the sperm to the gonopore). - Accessory glands are 1-3 pair, either mesodermal of ectodermal in origin and associated with vasa deferentia or ejaculatory duct. Its function is to produce seminal fluid and spermatophores (sperm containing capsule) Female reproductive system - The main function of the female reproductive system is egg production and storage of male\'s spermatozoa until the eggs are ready to be fertilized. - The basic components of the female system are paired ovaries, which empty their mature oocytes (eggs) via the calyces (Calyx) into the lateral oviduct which unite to form the common (median) oviduct. The gonopore (opening) of the common oviduct is usually concealed in an inflection of the body wall that typically forms a cavity, the genital chamber. This chamber serves as a capulatory pouch during mating and thus is often known as the bursa copulatrix. Its external opening is the vulva. In many insects the vulva is narrow and the genital chamber becomes an enclosed pouch or tube referred to as the Vagina. - Two types of ectodermal glands open into the genital chamber. The first is the spermatheca which stores spermatoza until they are needed for egg fertilization. The epermatheca is single and sac-like with a slender duct, and often has a diverticulum that forms a tubular spermathecal gland. The gland or glandular cells within the storage part of the spermatheca provide nourishment to the contained spermatozoa. - The second type of ectodermal gland, known collectively as accessory glands, opens more posteriorly in the genital chamber. - Each ovary is composed of a cluster of egg or ovarian tubes, the ovarioles, each consisting of a terminal filament, a germarium (in which mitosis gives rise to primary oocytes), a vitellarium (in which oocytes grow by deposition of yolk in a process known as vitellogenesis) and a pedicel. An ovariole contains a series of developing oocytes each surrounded by a layer of follicle cells forming an epithelium (the oocyte with its epithelium is termed a follicle), the youngest oocytes occur near the apical germarium and the most mature near the pedicel.  *http://www.entomologa.ru/outline/52.htm* **Insect Metamorphosis** Metamorphosis is a developmental change (change in form) - Series of events exhibiting different forms after hatching of eggs to adulthood in insects - Change in form during development - After hatching from an egg, young insects must molt in order to grow larger (exoskeleton too rigid for growth) - Most insects change body form as they develop - Young insects must molt in order to grow larger (exoskeleton too rigid for growth) Types: 1. Gradual metamorphosis = paurometabolous development (egg, nymph, adult) - Wings develop gradually as external, rudimentary wing pads into fully formed wings of adults - Immature stage, called nymph resemble the adults in type of mouthparts feeding on same food and form except for the absence of wings and reproductive structures. - Examples: Grasshopper, cockroach, leafhoppers, cicada 2. Incomplete metamorphosis = hemimetabolous development (egg, naiad, adult) - Occurs in aquatic insects where the immature stage has evolved specializations for life in the water having peculiar mouthparts, well- developed lateral or anal gills and peculiar body shape. - Nymphs are different from adults, are called naiads. - Naiads have external wing pads but breathe thru gills and feed on aquatic organisms. - Adults have 2 pairs of wings, breathe through spiracles, and feed on terrestrial organisms as predators. - Examples: dragonfly, mayfly 3. Complete metamorphosis=holometabolous development (egg, larva, pupa, adult) - Two stages of development between the egg and adult - Insect looks different from adult form in both the stages - Usually a larva (worm like) hatches from an egg - Larva eats almost anything & grows constantly doing considerable damage to plants. - Larva grows and molts several times before pupating. - Pupa -- developmental non-feeding, quiescent stage where larva changes into adult. - Pupa protected by a chrysalis -- an enclosed protective case. - Moths pupate in a cocoon. - Example: butterflies, moths, beetles, mosquitoes, true flies, bees, ants, wasps, 4. No metamorphosis =Ametabolous development (young, nymph, adult) - Insects undergo slight or no structural alteration as they grow older. - The immatures called young are the analogous with the adults in form, food, and habitat except in size and maturity. - Example: Collembola, Thysanura. Mallophaga, Anoplura Insect Reproduction The process of reproduction begins with courtship, continues with mating and ends with egg-laying. Methods of reproduction: 1. Oviparity -- eggs hatch after being laid, oviposition generally occurs soon after fertilization. 2. Ovoviviparity -- eggs are retained until they hatch and young larvae are deposited. Hatching occurs immediately after oviposition. 3. Adenotrophic viviparity- after hatching, the larvae are retained in the enlarged uterus, feed on maternal secretions and grow to full size, then pupate soon after deposition. 4. Pseudoplacental viviparity -- the egg develops in an enlarged pouch in which the embryo is nourished by specialized maternal and embryonic tissues which are fused or in close contact. Larvae Larval forms are highly variable in insects. However, there is sufficient similarity in overall structure to permit classification of type that is useful in describing their appearance. Types of insect larvae 1. Campodeiform - Body elongate, slightly flattened with well- developed legs; antennae and cerci usually with filaments on one end of abdomen. Mouthparts face forward, helpful when pursuing prey. Usually predaceous, quite active. - Diving beetle, Green lacewing, Caddisfly https://genent.cals.ncsu.edu/wp-content/themes/salient/img/growth/crawler.gif 2. Carabiform - Body same as campodieform with shorter legs, filament absent. - Carabid beetle, chrysomelid beetle 3. Eruciform - Caterpillars, body cylindrical, with a well-developed head capsule and very short antennae. Eruciform larvae have both thoracic (true) legs and abdominal prolegs. - Lepidoptera, Mecoptera,Coleoptera, Hymenoptera(Symphyta)  4. Scarabaeiform - Commonly called grubs, usually curved or C-shaped, and sometimes hairy, with a well-developed head capsule. They bear thoracic legs, but lack abdominal prolegs. Grubs tend to be slow or sluggish. - Coleoptera(specifically, those classified in the superfamily Scarabaeoidea https://genent.cals.ncsu.edu/wp-content/themes/salient/img/growth/grub.gif 5. Elateriform - Shaped- like worms, but with heavily sclerotized bodies; with short legs, and very reduced body bristles. - Coleoptera, specifically the Elateridae(wireworms) for which the form is named.  6. Vermiform - Maggot-like, with elongate bodies but no legs; may or may not have well-developed head capsules. - Diptera, Siphonaptera, Hymenoptera, Orthoptera, Lepidoptera, Coleoptera https://genent.cals.ncsu.edu/wp-content/themes/salient/img/growth/maggot.gif **Pupae** Pupal forms can be classified by means of the appearance of developing appendages. The pupae of insects with complete metamorphosis vary and three principal types are recognized. Types of insect pupae: 1. Obtect pupa - Appendages close to the body; held by tight-fitting outer envelope. - Found in Lepidoptera, Coleoptera and Diptera - Obtect pupa of butterflies are angular, maybe metallic colored called chrysalis  2. Exarate pupa - Appendages are free, not glued to the body, pupa looks like a pale, mummified adult, not covered by a cocoon. - Examples are pupae of Neuroptera, Trichoptera and Coleoptera https://genent.cals.ncsu.edu/wp-content/themes/salient/img/growth/exarate.gif 3. Coarctate pupa - Visible pupal case smooth, no apparent appendages, like exarate pupa but remaining covered by hardened exuviae of the next to the last larval instar called puparium. Occurs in Diptera