ENTOMOLOGY lect.docx

**ENTOMOLOGY** Insects are so much part of our environment. They are found everywhere -- in cities, parks, homes and gardens; buildings and conveyance, farms and forests; soil, air and water; and on bodies of man and domestic animals. This module presents the insects, their relatives, the differenc...

**ENTOMOLOGY** Insects are so much part of our environment. They are found everywhere -- in cities, parks, homes and gardens; buildings and conveyance, farms and forests; soil, air and water; and on bodies of man and domestic animals. This module presents the insects, their relatives, the difference between an insect and a mite, the characteristics that made them very successful group of arthropods, effects of insects to man and agriculture, recognition of insect orders, and representative insect pests of major crops. Entomology is defined as the scientific study of insects and related arthropods (Ross and Jacques, 1981). It originated from the Greek word "entomos" meaning "to cut" or "segmented" and "logos" meaning study. [Specialized Fields of Entomology] 1. **Insect morphology** deals with phylogenetic study of external and internal structures of insects and other arthropods 2. **Insect physiology** deals with comparative physiology of insects, its functional mechanisms and physiological bases of behavior 3. **Insecticide toxicology** deals with chemical and physical properties, formulations, biological effects and behavior of insecticides 4. **Insect taxonomy** studies classification, biology and evolutionary relationships among the higher insect taxa, including taxonomic methods and curating insect collections 5. **Insect ecology** studies the dynamics of insect population specifically their abundance, regulation, distribution and mensuration. It also deals with theories pertaining natural control of pest species 6. **Economic entomology** deals with bionomics and control of the major agricultural insect and mite pests of crop plants 7. **Veterinary entomology** deals with bionomics and control of insects and other arthropods which affect domestic animals 8. **Industrial entomology** deals with life history, behavior and utilization of insects, which provide products useful to man such as honeybees, silkworm and the like **Insects** and **mites** belong to the Phylum Arthropoda (Greek words: arthro = joint or segment; poda = foot/leg or appendage) - The arthropods make up about 80% of all animal species - Arthropods possess the following characteristics: (Baltazar and Salazar, 1979) a. bilaterally symmetrical; b. hard, chitinous exoskeleton; c. segmented body with paired segmented appendages; and d. sclerotized exoskeleton made up of chitin, a nitrogenous polysaccharide Under the phylum Arthropoda are two subphyla: a. **Chelicerata**: body divided into 2 regions: cephalothorax and abdomen; with 6 pairs of appendages. Near the mouth are the chelicerae- the first pair, and pedipalps - the second pair; the remaining 4 pairs are locomotory, without antenna (spiders, mites, ticks, scorpions, crabs, sowbugs) b. **Mandibulata**: head separate from the thorax; with a pair of well-developed mandibles acting as cutting and grinding structures with numerous modifications; head with 1 or 2 antennae and 3 or 4 pairs of feeding appendages or mouthparts. (insects, millipedes, centipedes) **Distinguishing characteristics of insects and their relatives (Phylum Arthropoda)** - Class Arachnida (spiders, mites, ticks, scorpions, etc) - Body regions: prosoma (cephalothorax) and opisthosoma (abdomen) - Prosoma: chelicerae, pedipalps, and 4 pairs of legs, with simple eyes, antenna absent - Opisthosoma: locomotor appendages absent - Class Crustacea (crayfish) - Body regions: varied; head and thorax covered dorsally by unsegmented carapace, and distinctly segmented abdomen - Appendages biramous (branched into 2) - Compound eyes on long stalk - Head appendages: 2 pairs of antennae, a pair of mandibles and 2 pairs of maxillae - Class Chilopoda (centipede) - With distinct external segmentation - Tagmata: head and trunk - Head: 1 pair of antennae, 1 pair of mandibles, 2 pairs of maxillae - Trunk: with 1 pair of leg per segments - Poison claws: appendages of the first trunk segment held beneath the head resembling mouthparts - Class Diplopoda (millipede) - External segmentation obvious - Head distinct with the following segment enlarged dorsally (collum) resembling those of the trunk; trunk composed of thorax and abdomen - Thorax poorly differentiated from head and abdomen - Thorax: with 1pair of legs on each of the 3 segments - Body segments have fused into pairs so that each apparent segment has 2 pairs of legs; Abdomen with 2 pairs of legs on apparent segments - Class Insecta - 3 body regions: head, thorax, abdomen - 3 pairs of legs in the adult stage - With 1 or 2 pairs of wings, some have none - 1 pair of segmented antennae - 2 kinds of eyes: (simple and compound) Insects and mites can be recognized based on their characteristic features. Characteristic feature Insects Mites ------------------------ ----------------------------------------------------- -------------------------------------------------------------------------------------------------------------- Body region (tagmata) 3; head, thorax, abdomen 2; cephalothorax (gnathosoma); abdomen (idiosoma) Wings 2 pairs of wings in adults; or wingless Wingless Antenna 1 pair Absent Eyes 2 kinds; Compound (1 pair) & Simple or ocelli (0-3) May be present or absent Characteristic feature Insects Mites Number of legs 6; 3 pairs 8; 4 pairs; larvae have 3 pairs Mouthparts mandibulate Chelicerate: having chelicerae (pincer-like feeding organ); pedipalp next to chelicerae, sensory in function Mites differ from other arthropods by the absence of abdominal segmentation. The diagnostic character that defines a mite is the destructive anterior gnathostome or mouth which is often modified or reduced. Arthropod pests, including insects and spider mites produce characteristic damage related to the way they feed, which is determined by the type of mouthparts they possess. **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). a. 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 b. 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 5 pair of wings. The plate bearing the wings is called pterothorax. The thorax is the locomotor segment of the insect c. 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 [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; and 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] 1. Usually a solid capsule (epicranium) without obvious segmentation due to the complete fusion of 6 or 7 primitive segments 2. Specialized for food gathering and manipulation, sensory perception and neural integration 3. **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 4. The head bears the eyes, a pair of antennae and the mouthparts 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] a. 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 b. 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 c. 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 - 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: a. acting as tactile organs; b. organs of smell (with olfactory receptors that detect odor molecules in the air) c. humidity receptors (detect changes in concentration of water vapor) d. organs of hearing (mosquitoes detect sounds) e. gauge air speed during flight (flies) The antennae are divided into three basic parts, namely: a. **Scape** - basal segment that articulates with the head capsule; contains intrinsic muscles and is generally larger than the other segments b. **Pedicel** - second antennal segment; nearly always contain a sensory organ called Johnston's organ c. **Flagellum or clavola** - remaining segments which respond to the movement of the distal part of the antennae relative to the pedicel Types of antennae: 1. **Setaceous** (bristle- like) -- segments becoming slenderer dorsal eg. Dragonflies and damselflies 2. **Filiform** (thread-like) - segments nearly uniform in size, usually cylindrical eg. Grasshopper, cockroaches 3. **Moniliform** (bead-like) - segments similar in size, more or less cylindrical eg. Termites 4. **Serrate** (saw-toothed) - segments particularly the distal half, more or less triangular eg. Female giant click beetle 5. **Clavate** (gradually clubbed) - segments gradually increase in size distally eg. Butterflies, carrion beetles 6. **Capitate** (abruptly clubbed) -- terminal segments are rather suddenly enlarged eg. Skin beetles 7. **Lamellate** -- the terminal segments expanded laterally to form rounded or oval plate-like lobes eg. Scarab beetles 8. **Flabellate** -- terminal segments with long, parallel-sided, sheet-like or tongue-like lobes extending laterally eg. Cedar beetle 9. **Pectinate** (comb-like) - most segments with long, slender lateral processes eg. Fire-colored beetles, Male glow-worms and Male giant click beetles 10. **Plumose** (brush-like or feathery) - segments with whorls of long hairs eg. Male mosquitoes 11. **Bipectinate** (double comb-like) -- all segments of both sides of the antenna are with long lateral processes) eg. Atlas moth Adult silkworm moth 12. **Geniculate** (elbowed) - first segment long, following segments small and going off at an angle to the first eg. Weevils and Ants 13. **Aristate** (pouch-like with usually dorsal bristle) - last segment usually enlarged and bearing a conspicuous arista eg. Houseflies Syrphid flies 14. **Stylate** the last segment bearing an elongate terminal finger-like process called style eg. Robber fly [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 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 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.