Insect Biology Notes PDF

# Lecture 2 - Sep 10 ## Parts of an Insect ### Head * **Major sensory organs** * **Antenna** ### Thorax * **Legs** - 3 pairs, attached to the 3 segments of the thorax * **Wings** - 2 pairs: * **Forewings** → mesothorax * **Hindwings** → modified into halteres on metathorax * **Mouthpar...

# Lecture 2 - Sep 10 ## Parts of an Insect ### Head * **Major sensory organs** * **Antenna** ### Thorax * **Legs** - 3 pairs, attached to the 3 segments of the thorax * **Wings** - 2 pairs: * **Forewings** → mesothorax * **Hindwings** → modified into halteres on metathorax * **Mouthparts** ### Abdomen * **Largest section** * **Major organs** ## Exoskeleton * **Chemically hardened** * **Surface for muscle attachment** * **Sensory interface with environment** * **Contains sclerites:** rigid plates of sclerotized (chemically hardened) cuticle * **Connected by suture:** line or groove marking union of two sclerites * **Compare to sulcus:** line marking an internal ridge of cuticle (apodeme) arising from invagination or infolding ## Segmentation * **Both thorax and abdomen show segmentation, but not on the head** * **Head:** fused "head capsule" * **3 oral segments:** * Labral * Antennal [antennas] * Postantennal (=intercalary) * **3 post-oral segments:** * Mandibular [mandible] * Maxillary [maxilla] * Labial [labia] → EACH HAS AN APPENDAGE * **Joint by sutures** ## Major regions: 1. Frons - front 2. Vertex - top of head 3. Occiput→ back of head 4. Gena - side of head below cheek ## Key things to notice: * **Frontoclypeal suture:** between frons and clypeus * **Labrum:** surrounded by 2 mandibles * **Below mandibles:** 2 maxilla * **Each maxilla bears maxillary palp [sensory function]** ## Mouthparts: * **Labrum - upper lip** * Formed by fusion of appendages present on either side of the mouth * Flap over mouth * **Mandibles - teeth** * Hinged to head capsule by 1-2 condyles * Archaeognatha: 1 condyle (monocondylic) * Thysanura: 2 condyles (dicondylic) * First pair of strong jaws * Lined by teeth * Move from side to side * Functions: chewing, cutting, tearing food * **Hypopharynx - tongue** * **Maxillae - guide food** * Behind mandible * Second pair of less powerful jaws * Move sideways * Functions: handle food, push food down throat * Pair of sensory palps → "maxillary palp" * **Labium - lower lip** * Covers mouth from behind * Moves longitudinally * Pair of sensory segmented palps → "labial palps" ## Mouthparts evolved by insect based on method of feeding: * **Chewing:** (e.g. Orthoptera, Dictyoptera, Coleoptera) * **Piercing and sucking:** (e.g. All Hemiptera; some Diptera) * **Sponging:** (e.g. some other Diptera) * **Rasping and sucking:** (Thysanoptera) | Feeding Type | Order | Example | | -------------------- | ----------------- | --------------------------------------- | | Chewing | Orthoptera | Grasshoppers & locusts | | | Dictyoptera | Cockroaches & praying mantis | | | Coleoptera | Beetles | | Piercing and Sucking | Hemiptera | True bugs & flies | | Sponging | Diptera | Housefly | | Rasping and Sucking | Thysanoptera | Thrips [asymmetrical mouth parts] | ## Locust: chewing (primitive) * upper lip - labrum * lower lip - labium * 2 mandibles * 2 maxilla * Labia and maxilla bear sensory palps → tasting ## Cicada/true bugs and flies: piercing and sucking (modified) * 2 mandibles and 2 maxilla are sharp and pointed sucking tube called proboscis (enclosed in sheath formed by labium) ## Mosquito: piercing and sucking (modified) * Labrum, 2 mandibles, 2 maxilla, & hypopharynx form 6 stylets → pierce skin when feeding blood * Enclosed in sheath formed by labium, when feeding, come out of sheath * Saliva: antihemostatic, anticoagulant, vaso-dialator (continuous supply of blood) ## Bees and wasp: chewing and lapping (modified) * Maxillae + labium form sucking tube called proboscis * Saliva discharged, nectar drawn up ## Hemiptera: mouth parts involved in functions besides eating * Cleaning, moving stuff, molting act like hands ## Butterflies & moth: siphoning (modified) ## Horsefly: * Maxillae form sucking tube (proboscis) * Mandibles & hypopharynx absent, labium reduced, + labial palps reduced ## Diptera ### Housefly: * Piercing and sucking * Mandibles curved, slash into skin of horse * Maxilla sharp and pointed, drill into body of host * Create wound, blood comes out * Labium forms sponge that sucks blood ### Sponging * Sponge formed by labium * Absent mandibles * Maxilla bear unjointed maxillary palps ## Butterfly: * **Labial palp- ## Mosquito: ## Cicada: ## Honeybee: * *some immature (larval) insects, the only sclerotized part of the body is the head capsule* → support muscles involved in chewing the food ## Orientation of mouthparts: 1. **Hypognathous** (mouthparts project downward) * a. e.g. Orthoptera - grasshoppers and locust # Lecture 3 - Sep 12 ## The thorax, abdomen, wings and legs ### Pro-, meso- and metathorax * Each bears a pair of legs * Meso and metathoracic segments each bear a pair of wings ### Abdomen * Midsection divided into 3 sections: * anterior * META * PROTHORAX * MESOTHORAX * METATHORAX ## Ventral plate: sternum (bottom) ## Lateral plates: pleuron (side) ## Notum divided into 2 regions: * **Alinotum - bears wings:** divided into 3 regions 1. Prescutum 2. Scutum 3. Scutellum (posterior) * **Postnotum - bears phragma → intersegmental fort:** flight muscles are attached ## Sternum divided into 2 regions ### Sternum: 3 regions 1. Presternum 2. Basisternum 3. sternellum 4. Spinesternum: 2 plates divided by pleural suture (marks location of internal ridge of exoskeleton, strengthens side of thorax) * Ventral end: pleural suture forms point of articulation with coxa of leg * Runs dorsally an articulates pleural wing process: finger-like plate, serves as fulcrum (lever) for base of wing ### Episternum ### Epimeron ## Most insects have 3 pairs of walking legs * 1 pair on each thoracic segment * Each leg: 5 structural segments articulate with one another by means of joints ### 1. Coxa: proximal segment * Attached to body of insect * Heavy, round, short ### 2. Trochanter * Provides wide range of motion ### 3. Femur * Reduces power * Highly muscular ### 4. Tibia * Lined by spines * Kicking device ### 5. Tarsus * Divides into 5 segments: "tarsomeres" * Number of tarsomeres may be reduced * Last segment: "pretarsus: extended between claws * Claws: sometimes other structures present between claws * Pad or bristles * Pad: sticky substance, help insects stick to surfaces ## Grasshoppers + locusts: legs modified for jumping ## Praying mantis: forelegs modified for holding stuff ## Mole crickets: forelegs modified for digging ## Giant water bug: hindlegs modified for swimming ## Cockroach: legs modified for running ## Some insect larva: short fleshy legs present on one or more abdominal segments * Have barbs used to grip substrate * Abdominal prolapse never occurs in adult stage only larvae (not true legs) * True legs only present on thorax of insects ## Swimming * aquatic Hemiptera and Coleoptera ## Jumping * Orthoptera, some Hemiptera, fleas ## Grasping Prey * mantids, giant water bug ## Grasping Hosts * lice; other ectoparasites ## Digging * scarab beetles, some crickets ## Sound production * some grasshoppers ## Cleaning, carrying pollen * honeybee ## Defense * some leaf insects ## Joined rigidly, form box that houses muscles for legs and wings ## Each section has: * **Dorsal plate: notum (top)** # Lecture 4 ## Reproduction, Embryology and post-embryonic development in insects ### Means of locating mates ### Courtship behaviors ### Insemination, fertilization ### Post-copulatory behaviors ### Embryological development ### Larval development ## Mate Location * "Females and males need to be in the same place at the same time" ### On a host: * **Strepsiptera** (twisted-wing parasite) * females legless * wingless * internal parasites of bees (only the tip of the abdomen is exposed) ### At a food source: * **face flies** (Muscidae) * attracted by the olfactory eminations of cowpies (this is where they mate and females oviposit) ### Lek behavior: * male dragonflies, tiger moths (Arctiidae), certain bees, and *Drosophila* * defend territories on a common mating ground ## Courtship behaviours * Give females gifts or empty box * Females take males on long flight to test their fitness, so male adapted to want to mate as soon as females emerge from pupa to avoid this. ### Host plant for ex twisted wing parasite (image) * Male can fly * Female spends life inside body of host (bee) * Males locate female because abdomen exposed on body of host, male finds it and mates with her ### Attracted to smell of food source (cowpies), find each other + mate & female lays eggs ### Lek = common mating sites, select area, all males move there, mark territories, females arrive later + have plenty of opportunities to find male ### Hill topping behaviour: males sit on cliff on high place and find each other easily *--> butterflies ## Visual displays: - butterfly courtship - fireflies (light emissions) - fruit flies ## Chemical attractants: (pheromones) * mate location over long distances (>1 km); best studied in moths ## Sound production: * special structures for stridulation in Orthoptera (e.g. crickets) and some aquatic Hemiptera (Corixidae) * male mosquitoes are attracted to the specific frequency of female mosquito wingbeats # Lecture 5 ## The integument, molting and endocrine control * Morphology and chemistry of the insect integument * Sclerotization of insect cuticle * Physical aspects of molting * Endocrine control of molting and development ## Epicuticle: * provides waterproof layer ## Exocuticle: * hardened by sclerotization ## Endocuticle: * not sclerotized; resorbed during molting ## Epidermis: * produces all the above layers ## Molting: a 3-stage process 1. **Apolysis** - separation of the epidermis from the cuticle of the previous stage 2. **Ecdysis** - casting off (or escape from) the residual cuticle of the previous stage. A fully formed insect inside the old cuticle prior to ecdysis is called a pharate. The cast cuticle is called an exuvium. 3. **Sclerotization** - chemical process that hardens the outer section of cuticle. Until sclerotization is complete after the final molt, the insect is referred to as a teneral adult. # Lecture 6 ## Insect Nutrition - the Basics * "What an insect needs" ### 10 essential amino acids * (like rats and humans) * phenylalanine * important for larval growth * some insects can "spare" deficient amino acids * alternative aa serves non-specifically in same capacity ### Cyclitols * myo-inositol * membrane synthesis (esp. plant feeders) ### Fat-soluble vitamins * vitamin A complex - vision * vitamin B complex * vitamin D complex * vitamin E complex * vitamin K complex * vitamin H complex * vitamin C complex ### Free fatty acids (C18)(oleic, linoleic acids) * many lepidopterans cannot pupate * adults - wing deformities (slight defficiency) ### Sterols. * Insects cannot synthesize sterols * Plant feeding insects modify phytosterols to cholesterol * essential for * synthesis of ecdysteroids (molting hormones) * surface waxes of the epicuticle * membrane production * development for each essential amino acid # Lecture 7 ## Dietary Utilization by Insects ## (Quantitative Nutrition) * **Nutritional parameters** * Major requirement -optimal growth * **Compensation for reduced diet** * **Nutrient Self-selection** ## Dietary Utilization by Insects ## (Quantitative Nutrition) * **Insect nutrition - two ways:** * Nutrients essential for growth and development? * study of isolated phenomena * Efficiency of converting ingested food into their own biomass? * considers ecological constraints * evolutionary specialization * **Methodology -very simple (gravimetic)** * yield very interesting and useful information # Lecture 8 ## Insect Respiration and Circulation * **Respiratory system** * **Spiracles** * **Trachea** * **Tracheoles** * **Taenidia** * **Air sacs** * **Active ventilation** * **Passive ventilation** * **Cyclical burst** * **Functions of trachea including additional functions** * **Arrangement of spiracles** * **Adaptations in aquatic insects see examples** * **Circulatory system** * **Hemolymph** * **Hemocoel** * **Dorsal blood vessel{multichambered heart +aorta}** * **Pericardial sinus** * **Perineural sinus** * **Local pulsating organs** * **Functions of hemolymph** * **Phasmatocytes** * **Hemocytes** # Lecture 9 ## Excretion and water balance (numbers not needed, need to know the concept). Diagrams are to help you understand the phenomenon, you will not be asked to draw or label anything. * **Organs of excretion (Malpighian tubules and hindgut)** * **Euryhaline and stenohaline insects** * **Examples of insects maintaining osmoregulation** * **Cryptonephridium** * **General nature of the excretory process** * **Fate of toxic compounds (sequestered, used for nutrients, synthesis of pheromones, eliminated from the body etc.)** * **Role of hormones (Diuretic hormone and antidiuretic hormone)in maintaining water balance in the body** * **Diuretic hormone (DH):** synthesized in the median neurosecretoy cells (mNSC) in the brain and stored in a gland known as Corpora Cardiaca (CC), proximate stimulus for the release of this hormone is gut/abdominal distension, causes diuresis or urination in insects. If homogenate of mNSC or CCor the hemolymph from a blood-fed bug is injected into an unfed blood, this will cause diuresis because the homogenate contains DH. If mNSC are destroyed, this will cause swelling in insects as the source of DH is destroyed. * **Antidiuretic hormone (ADH)-causes rectal absorption of water (prevents water loss), triggered by dehydration Produced by mNSC in the brain of an insect and stored in CC (corpora cardiaca)** # Lecture 10 ## Feeding and Digestion * **Salivary glands-piercing/sucking mouthparts** * **Saliva of bloodfeeders (e.g. mosquito)** * local anesthetics, vasodilators and anticoagulants * **Saliva of sucking plant feeders (Hemiptera)** * digestive enzymes * amylase or invertase * **Aphid saliva - pectinases** * facilitate penetration of the stylets * plant tissues -vascular tissues (phloem) * **Many insects require microbial symbionts for adequate nutrition** * Transferred on eggshells * eaten by neonates * Sequestered cellulases from fungi (wood wasps - Siricidae) * Lower termites (wood feeders) * obtain cellulase activity from enteric protozoa and bacteria * thrive in an anaerobic region of the hindgut called the paunch. * Termites reared under aspectic conditions - alive but do not grow * **Control of digestion** * **Digestion** * enzyme secretion in the midgut * **Secretion regulated by** * **Secretagogue** - an enzyme stimulating substance in the food * **Neural stimulation** - stretch receptors in the midgut -presence of food * **Hormonal stimulation** - response to nutritional state of the insect * **Rate of digestion is often determined** -rate of degradation-polysaccharides to monosaccharides # Lecture 11 ## Endocrine control of excretion/water balance * **Rhodnius:** * hemolymph from bloodfed bug → unfed bug * stimulates diuresis * **Cauterizing mNSC cells in brain** * causes insects to swell (no diuresis), * injection of mNSC or CC homogenate * stimulates diuresis * **Proximate stimulus - gut/abdominal distension** * **Diuretic hormones:** * a group of neuropeptides ranging in size from 1000-2000 daltons * More potent form -corpora cardiaca * form produced in the brain is a precursor # Lecture 12 ## Major organs: Malpighian tubules and Hindgut ### Malpighian tubules (Marcello Malpighi-17th century) * main excretory organ * blind-ended tubules ~ 100 μ dia. * single layer of epithelial cells * Size 2-70 mm * composed of 3 cells (cross-section) * numbers of tubules 2-250 * Hemiptera -4, locust-200 * absent -aphids and collembola * tubules differentiated histologically -up to 4 distinct sections * surface area proportional to body size: 0.54+0.22 mm²/mg body wt * low operating sytem-secretion of primary urine * minimal energy expenditure * Main function: * Removes nitrogenous waste-uric acid (>80%) ### Antidiuretic hormones * rectal absorption of water * Homogenates of corpora cardiaca or ventral ganglia stimulate up to 5-fold increase of resorption -ileum of locusts * Based on Cl-pump * Stimulated by CTSH (chloride transport stimulating hormone---only active in rectal tissues) * ITP (ileal transport peptide) ## Role of proline * Malpighian tubules * active secrete proline * actively reabsorped -rectum * energy source (respiratory substrate) * drive active transport (e.g. Cl-pump)- rectum tissue * secreted by the Mt's -mitochondria of the hindgut * hindgut cells have a specific proline carrier # Lecture 13 ## Excretion and water balance in the insect * **Malpighian tubules secrete** * sugars, amino acids (especially proline), water, KCI, toxins and nitrogenous wastes * **Primary urine -Mt's into the hindgut (ileum, colon and rectum) -resorption** * **Water resorption in the rectum** * **Sugars, amino acids and ions - resorbed in the hindgut** * **In locust, 95% of Mt fluid -resorbed** * **Tenebrio has a cryptonephridium:** * distal ends of Mt's fused with the rectal wall * urine recycled several times * Midgi * almost complete recovery of water -feces * **some desert beetles are -absorbing atmospheric moisture-their rectal walls** # Lecture 14 ## Respiratory System of Insects * **Insects breathe through spiracles** * Small holes in their abdomen * Air enters the spiracle allowing oxygen to travel along a network of tubes called trachea to reach the cells in the insects body # Lecture 15 ## Circulatory System of Insects * **Insects have an "open" circulatory system** * **hemocoel** (body cavity) * **hemolymph** (blood) that bathes the organs * **Circulatory organs include the multichambered 'heart' and the aorta (dorsal blood vessel)** * Number of chambers varies between species: Cockroach has 13, house fly has 3 * Each chamber has a pair of ostia inlet valves that draw hemolymph into the heart * **Insects also have 'local pulsating organs'** * bases of wings, legs and antennae * Antennal artery x 2 * Aorta * Frontal aortal sac * **Functions of hemolymph** * Most important: transport of nutrients, wastes, hormones * Water storage * Lubrication of internal organs * Heat exchange - wings act as solar collectors * Hydraulics - molting, wing expansion, active ventilation, leg/antennal movement * Protection from microorganisms, parasites * Defense - reflex bleeding * **Does not carry 02!** * Most important: carrier nutrients for transport!! * Prevent friction * Trachea holds in place but hemolymph prevents friction * **Ladybug beetle (also plays dead)** * When threatened, secrete droplets of hemolymph * Smells bad * Smell it and predators run away (why? Something about smell?) # Lecture 16 ## Excretion and Water Balance in Insects * **Requirements of the system** * **Organs involved** * **Endocrine control** * **Like most animals, insects must (1) maintain a reasonably constant blood composition and total water content for cell viability (=homeostasis), and must (2) eliminate toxic wastes** * **Osmoregulatory challenges more extreme -insects** * **Euryhaline mosquito larvae:** * fresh water to 300% sea water (tide pools/marshes) * alkaline salt lakes at pH > 10 * larvae harvest dilute food from pond sediments * hemolymph osmotic concentration (NaCl levels) vary less than 2-fold over > 1000-fold change in external salinity # Lecture 17 ## Endocrine control of excretion/water balance * **Some insects feed on plants** * high levels of toxic compounds, * Manduca - tobacco (nicotine) * Oncopeltus-milkweed (digitoxin-type cardiac glycosides) ## General nature of the excretory process: 1. **Eliminate most blood solutes non-selectively;** takes place in the Malpighian tubules 2. **Selectively reabsorb useful solutes;** takes place mostly in the hindgut 3. **Actively excrete certain toxins (Malpighian tubues)** # Lecture 18 ## Major organs: Malpighian tubules and Hindgut ### Malpighian tubules * **Malpighian tubules (Marcello Malpighi-17th century)** * main excretory organ * blind-ended tubules ~ 100 μ dia. * single layer of epithelial cells * Size 2-70 mm * composed of 3 cells (cross-section) * numbers of tubules 2-250 * Hemiptera -4, locust-200 * absent -aphids and collembola * tubules differentiated histologically -up to 4 distinct sections * surface area proportional to body size: 0.54+0.22 mm²/mg body wt * low operating sytem-secretion of primary urine * minimal energy expenditure * Main function: * Removes nitrogenous waste-uric acid (>80%) ### Antidiuretic hormones * **rectal absorption of water** * **Homogenates of corpora cardiaca or ventral ganglia stimulate up to 5-fold increase of resorption -ileum of locusts** * **Based on Cl-pump** * **Stimulated by CTSH (chloride transport stimulating hormone---only active in rectal tissues)** * **ITP (ileal transport peptide)** ## Role of proline * **Malpighian tubules** * active secrete proline * actively reabsorped -rectum * **energy source (respiratory substrate)** * **drive active transport (e.g. Cl-pump)- rectum tissue** * **secreted by the Mt's -mitochondria of the hindgut** * **hindgut cells have a specific proline carrier** ## Time taken for total extracellular fluid to be filtered by glomeruli of vertebrate kidney or Malpighian tubules of insects | Animal | Time (min) | | ------- | ---------- | | Human | 135 | | Rat | 42 | | Dog | 57 | | Chicken | 138 | | Dysdercus | 1500 | | Schistocerca | 1700 | | Aedes | 2000 | ## Malpighian tubules secrete * sugars, amino acids (especially proline), water, KCI, toxins and nitrogenous wastes * **Primary urine -Mt's into the hindgut (ileum, colon and rectum) -resorption** * **Water resorption in the rectum** * **Sugars, amino acids and ions ** - resorbed in the hindgut * **In locust, 95% of Mt fluid -resorbed** * **Tenebrio has a cryptonephridium:** * distal ends of Mt's fused with the rectal wall * urine recycled several times * Midgi * almost complete recovery of water -feces * **some desert beetles are -absorbing atmospheric moisture-their rectal walls** # Lecture 19 ## Nutrient Self-Selection * **Insects regulate their food intake based on the nutritional value of the food.**