Entomology 1.oo3 Entomology: Structure and Life Process 1 Entomology: Structure and Life Processes Matthew J. Grieshop MSU Department of Entomology 2 Insect Facts The major consumers of plant biomass 200 million insects per person As much as 400 lbs of biomass per acre Only 14 lbs of human biomass 3 Insect History Earliest Arthropods: 530mya cambrian seas Earliest Terrestrial fossil: 428mya millipede Devonian Earliest Flight: 400mya? Devonian Insects have been around a long time Intricately linked to the evolution of angiosperms (pollination). Intricately linked to plant evolution in general (as consumers) and vertebrates (as parasites, vectors, and food) 4 Recall Tagmosis Insects are segmented! Segmented tagma, segmented appendages, specialized functions Insects have 3 Tagma, each with specialized functions Head: Sensory, Feeding, Defense Many segments: few distinct. Thorax: Locomotion, Sensory?
Three distinct segments (Pro, Meso, Meta -thorax) Attachment of legs (also segmented antennae and eyes) Abdomen: Digestion, Reproduction, Defense? up to 11 distinct segments 5 The Integument Insects have an exoskeleton The Integument is layered Sclerites make up the armor plates of the exoskeleton seperated by membranes Basement Membrane Epithelium Endocuticle Exocuticle Chitin: Polymerized polysaccharide + protein Very tough, hard to digest also present in fungal cells Epicuticle Wax, Cuticulin 6 The Head The insect head is composed of many sclerites joined by sutures Vertex, Gena, Frons (important sclerites) Compound Eyes, Ocelli, Antennae, and mouthparts are located on the insect head. 7 Mouthparts Just as in Nematodes what insects eat affect what they use to eat Handy for identification both and functional
Insects are Mandibulate this especially apparent in insects with chewing mouthparts Mandibles Maxillae and Palps Labrum Labium Sucking mouthparts are also common The same structures are present but highly modified 8 Sucking Mouthpart function Typically sucking mouthparts have a salivary channel and a food channel The Labium becomes a sheath and the mandibles, and maxilla become stylets Stylets move in opposing directions to penetrate a host Salivary glands produce saliva that helps feeding Food is returned via the "food canal" 9 Antenna Antenna are used by insects for olfaction Antenna Are also segmented Scape, Pedicel, and flagellum Many types of antenna filiform serrate clavate pectinate plumose 10 The insect Thorax Pro- Meso- Meta- segments
All bear legs Meso and Meta bear wings (in flying insects) Notum: Top Sternum: Bottom Pleura: Sides 11 Insect Legs Also segmented Coxa Trochanter Femur Tibia Tarsus Pretarsus Leg structure tells us a lot about how insects move and their feeding habits Pretarsus tells us alot about what substrates insects use 12 Insect Wings Almost all insects have wings or wing derived structures (pterygota) Primitive wingless insects are denoted apterygota Wings are membranes supported by wing veins Very important in insect identification 13 The Abdomen Abdomen ranges from 6 to 11 segments Tergum: Top Sternum: Bottom Lateral Membrane: Sides Terminates in a Paraproct
May have Cerci Ovipositor on females Aedeagus on males 14 Internal Morphology Insects can be characterized as a chitinous sack filled with hemolymph and organs Circulatory System is Open Digestive, Nervous, and Respiratory systems are closed 15 Digestive Tract Three main sections to alimentary canal Foregut: Ectodermal in origin has Chitin Pharynx: Throat Esophagus: Gullet Crop and Proventriculus Midgut: Endodermal in origin lacks Chitin Hindgut: Ectodermal in origin has Chitin Ends in Rectum and Anus Malpighian Tubules: Insect Kidneys Join at front of hindgut Critical for water balance and excretion of digestive wastes 16 Insect Digestion Extraoral digestion Most insects begin digestion outside the alimentary canal Foregut: Food is exposed to more digestive enzymes and ground by the proventriculus Midgut: Extensive enzyme activity
Hindgut: Excretion and water reabsorbtion Gills in some insects 17 Insect Circulatory System Dorsal Vessel consisting of a Heart pumps blood forward to the Aorta Aorta dumps blood into head capsule (feeds the brain) Ostia draw in blood from thorax and abdomen of the insect Midgut, Malpighian Tubules, Endocrin System, and Brain all "floating in blood" and absorbing or excreting into the. 18 Respiration System Tracheal system: a network of tubes that diffuse gas throughout the insect body Spiracles: openings on the thorax and abdomen Tracheal Trunks: Large tubes that run laterally and connect with Tracheoles 19 Insect Nervous system Central Nervous System: Brain, ganglion, visceral nervous system Brain consists of the Proto-, Deuto-, and Trito- cerebrums Proto: ennervates the eyes Deuto: ennervates the antennae Trito connects with the Subesophogeal Ganglion and thoracic and abdominal ganglia Subesophogeal Ganglion and Visceral nervous system Subesophogeal Ganglion: Mouthpart ennervation Frontal Ganglion: Thoracic and abdominal Ganglia
Corpora cardiaca and corpora allata: Neurosecratory glands (produce hormones that control physiological processes). 20 Insect Locomotion Insects walk, swim, and fly Flight is accomplished through the use of direct and indirect flight muscles Indirect flight muscles are more efficient and more common Expansion and contraction of the meso and meta thoracic segments used to "pop" wings up and down. Dorso-lateral and muscles 21 Insect Reproduction Females have Ovaries Special structure called a Spermatheca maintains sperm within the female reproductive tract allows one by one egg fertilization and sex determination in some species Eggs are formed in a process called oogenisis Males have Testes Sperm are formed in a process called spermatogenisis 22 Insect Metabolism Insects are cold blooded or "endotherms" This means that the rate of metabolic processes are largely determined by ambient temperatures. Thus insects are more active in warm temperatures and actually age faster
Consequence: Insects are distinctly tied to seasonal patterns and climate 23 Molting Insects must shed their cuticle to grow This process is called molting and is controlled by insect hormones In effect a new cuticle is formed under the old, the old cuticle splits and is sloughed off. Much of the old cuticle is digested by special enzymes during the molting process and the remainder is often times it is eaten to recapture nutrients Actual shedding of the old cuticle is called ecdysis Eclosion refers to insect emergence from pupal to adult Once the new skin is formed it must sclerotize to harden 24 Insect Life Cycles Two basic life cycles: Hemi- and Holo- metabolism Hemi- have three distinct life stages Egg, Nymph, Adult Holo- have four distinct life stages Egg, Larva, Pupa, Adult Metamorphosis Metamorphosis allows larva to focus on feeding and resource transformation and adults to focus on dispersal and reproduction. Adults and larva rarely compete.