Insect Muscular System (CPROT 4205) PDF

7. MUSCULAR SYSTEM MUSCLES Movement of the insect’ body and its -Occur or appear in antagonistic appendages is produced by an intrinsic pairs: if there is a flexor, there is an system of musculature. extensor Muscle cont...

7. MUSCULAR SYSTEM MUSCLES Movement of the insect’ body and its -Occur or appear in antagonistic appendages is produced by an intrinsic pairs: if there is a flexor, there is an system of musculature. extensor Muscle contraction is facilitated by nerve -Biological machines which convert impulses at nerve endings. chemical energy into mechanical work and into heat The coordinated movement of muscles and appendages is critical to important activities PRINCIPAL TYPES OF INSECT like feeding, walking, jumping and flying. MUSCLES MUSCLES are made up contractile units - Based on the arrangement and number of called myosin filaments. These are striated myofilaments, nuclei and the way how the fibers. fibers are embedded in connective tissue striated = with light and dark bands 1. Typical e. g. honeybee larva (isotropid and anisotropid bands) made up of actin and myosin filaments; characterized - fibrils only slightly differentiated, by the presence of numerous nerve endings enclosed in thick layer of superficial from a single axon (multiterminal plasma; nuclei found within the plasma innervation) layer(fibrils= a small filament or fiber) Fibers = myofibrils situated in a matrix of 2. MICROFIBRILLAR e.g. leg muscles of multinucleated cytoplasm. Along with the Orthoptera,, Trichoptera and Lepidoptera myofibrils are mitochondria which contain enzymes for the oxidation process that -fibrils closely packed, interspersed with release free energy for muscle reaction. columns of mitochondria; each fiber surrounded by sarcolemma; nuclei Myosin filaments peripheral – protein, long coiled chains of Sarcolemma – plasma membrane polypeptides Sarcoplasma – plasma Sarcoplasm - cytoplasm - Have lateral projections which interlink with actin filaments 3. Lamellar or tubular e.g. direct flight during contraction muscles; nuclei found only along the central portion forming a column and -With cross bridge, double helix surrounded by alternating rows of mitochondria and fibrils; more mitochondria indicating the need for more energy  - Longitudinal bands connect the tergites and sternites in the abdomen 4. Fibrillar - of large diameter fibril surrounded by - Tergites to sternites of same segment are sarcolemma connected by oblique muscles on each side of the body - In between fibrils are mitochondria and sarcoplasm; nuclei peripheral - In the thorax, predominant muscles are large cordlike bands moving the legs and - Found in indirect flight muscles of very wings efficient fliers (located along dorsum, thorax) - Appendage muscles - Presence of a large number of - Movable appendages have muscles either mitochondria indicating the use of a lot of in them or attached to them energy during flight e.g. legs = attachment for muscles housed - Lots of cytochrome C, glycogen; well in the body tracheated and ventilated = attachment for muscles housed directly in the appendage CATEGORIES OF MUSCLES OF INSECTS - Body muscles generally move the whole appendage, the segmental muscles move - Visceral muscles parts of the appendage - Occur in circular, longitudinal or oblique LOCOMOTION IN INSECTS bands around the digestive tract = produce peristaltic movements of the gut that moves A. WALKING – basic mode of locomotion of food and wastes along its length insects on land - Specialized muscles associated with the TRIPOD MANNER for adult insects spiracles 1 = 2 legs on the ground on one side - Others cause peristalsis or contractile movement of the heart 1 leg on the ground on the other side - Segmental muscles 2 = 3 other legs raised as - Series of bands that connect body 3 = grounded legs push backward segments Alternation of pushing tripods results in a slightly zigzag path of forward motion Maybe modified: LOCOMOTION IN INSECTS FLYING - Single-leg movements in very slow- walking insects - In more primitive insects (dragonflies, roaches, beetles): - In praying mantids, 1st pair of legs is not used for walking - up-and-down beat cycle B.CRAWLING - basic mode of locomotion - Begins with contraction of the dorsoventral for worm-shaped immatures (larvae) muscle (indirect flight muscles) 🡪 depression of the tergum forcing wing base As the caterpillar inches its way forward, down and the wing up, with the thoracic longitudinal and dorsoventral muscles pleurite as fulcrum oppose each other in each segment - In the next cycle, contraction of basalar Synchronized operation produces a wave of muscles (direct flight muscles) and contraction down the body relaxation of dorsoventral muscles (indirect flight muscles) forces the wing Fleshy prolegs on abdominal segments down, and the tergum is raised assist in anchoring the abdomen. This will prevent the body slipping backward and -In more advanced fliers, e.g. honeybees causes the body to move forward - Up-and-down movement is produced only For loopers, crawling is accomplished in a by indirect flight muscles (dorsoventral and sort of looping motion. Prolegs are brought dorsal muscles) that cause flexing of the forward and anchored causing a loop in the thoracic segment and produce wing beat abdomen, followed by a straightening of the whole body - In addition, wings display a synchronized rotation C. FLYING = only adults can accomplish flight (exception: in mayflies, weak flights - Result: more surface on the downstroke may occur just before full sexual maturity) than the upstroke pushing air backward to cause forward movement - Muscles in the thorax are involved in flight: - This is accomplished by muscles that - Indirect flight muscles attached to tergites distort the tergum and others that apply and sternites pressure alternately to the front and back of the wings - Direct flight muscles attached to wing bases  - e.g. eyes as the most complex photoreceptor involved in forming images 8. THE SENSES OF INSECTS - COMPOUND EYES (CE) For insects to exist, they MUST SENSE the realities of the environment and govern their - perceive images, color, movement activities accordingly. They must locate food, find mates, avoid enemies, make - not found in primitively wingless insects nests and perform internal functions. They (have evolved along with flight); Lacking in accomplish these tasks only by perceiving immature of most advanced insects; Most conditions and integrating this information to insects with CE also have simple eyes perform the appropriate behavior. - Principal visual organ, characterized Perception is achieved by a number of externally by the cornea being divided into different sense organs, and behavior results hexagonal facets. Each facet is part of the from integration of information and individual sensory units called ommatidium. stimulation by the nervous system. NOTE: THE SENSES OF INSECTS … THE NUMBER OF FACETS TO A CE - BASIC SENSES VARIES 1. SIGHT - 20,000 in dragonflies 2. SMELL (OLFACTION) - 12,000 or more in Lepidoptera 3. TASTE (GUSTATION) - 4,000 in Musca (house flies) 4. TOUCH - Fewer than a dozen in workers of 5. HEARING certain ants - GROUPS OF ORGANS/RECEPTORS STRUCTURE OF THE CE/HOW THE CE (ECTODERMAL IN ORIGIN) WORKS 1. PHOTORECEPTORS Light is gathered in ommatidium by lens or 2. CHEMORECEPTORS cornea 3. MECHANORECEPTORS 4. AUDITORY ORGANS The lens focuses light thru a crystalline 5. TEMPERATURE AND cone (CC) to a light-receptor apparatus HUMIDITY RECEPTORS (LRA). [The LRA comprises 6 – 8 retinula cells (RC) which combine to produce a PHOTORECEPTORS central light sensor (rhabdom). The CC and LRA are surrounded by pigment cells that - Detect presence and quality of incident isolate to various degrees, 1 ommatidium light; when images are produced it is called from another] sight. RC turn light into electrical energy which is carried to nerve fibers by the brain. - May occur singly (e.g.sawfly larvae) or in Images produced by ommatidia are groups on either side of the head (e.g. believed to result in an overall mosaic Lepidoptera larvae) object, each ommatidium supplying only a piece of vision. NOTE: SOME INSECTS HAVE NO EYES, THUS THEY DETECT LIGHT THRU THE SIMPLE EYES/OCELLI CUTICLE (DERMAL PHOTORECEPTION) - Present in many immatures of CHEMORECEPTORS Endopterygota - Detect the presence of chemical - Also believed to perceive images although substances in the air thru the sense of smell probably produce a less complete mosaic; (OLFACTION) OR on substrates thru the some appreciation of color; perceive sense of taste (GUSTATION) movement of objects in their vicinity; responsible for orientation to light - Based on the detection of certain molecules by receptor organs that - Some insects with only simple eyes scan subsequently produce a nerve impulse environment by moving head back and forth FORMS OF CHEMORECEPTORS - Structure varies among insects - short pegs or hairs on various body parts - Some similar to individual ommatidia (antennae,palps) (caterpillars) TASTE RECEPTORS - Some with a single cornea overlying several retinula cells and rhabdoms - Contact chemoreceptors prevalent on surfaces of mouthparts, antennae (some SIMPLE EYES Hymenoptera) and tarsi (Lep, Dip, honeybees); sensilla usually hairs or - distinct from the CE thru the presence of a cones with 4 neurons single corneal lens - Sense molecules from liquids 2 classes: - Have fine nerve endings exposed to the - Dorasl ocelli of imagines and nymphs environment at hair tips - 3 arranged in a triangle on frontal region of In general, wide differences in taste head or on the vertex thresholds of different substances with a given species and for different species with - Lateral ocelli of most endopterygote larvae the same substance happen sugar solution ] [ preferred to distilled H2O dilute acid/salt - No general uniformity of structure soln]  vibrations by long, slender, more conc acid,salts soln ] trichoid sensilla 🡪 rejected [ esters, alcohols,amino acids ] - FOR THE TYMPANUM to vibrate = SMELL RECEPTORS perceived by chordotonal organs made up of scolopidia - Perceived by olfactory sensilla characterized by the presence of numerous Where is the tympanum? pores -In grasshoppers, on 1st abdominal - Peglike; have greater number of nerve segment endings at the surface -In crickets, on tibiae - Most numerous on insect’s antennae, also abundant on palpi of mparts -In moths, abdomen and metathorax - More numerous on males: e.g last 8 Johnston’s organ in the pedicel of adult antennal segments in male Apis about insects responds to movements of 30,000 sensilla compared to workers = antennae; maybe involved in hearing 6,000 & queens = 2,000 - SENSILLA _ COELONICA, - Play an important role in the life of CAMPANIFORMIA insects since many behavioral and - SENSILLA _ CHAETICA developmental changes are caused by - SENSILLA _ TRICHOIDEA pheromones - SENSILLA - BASICONICA - pheromones – highly specific, 9. THE INTEGUMENTARY SYSTEM volatile substances perceived thru the olfactory sensilla after being secreted INTEGUMENT OR BODY WALL by other members of the same species -Outer covering of the living tissues of - e.g. Scents produced by virgin females insects; sclerotized for protection from of some moth attract the males abrasion as well as waterproofing -Composed of a single layer of cells called MECHANORECEPTORS EPIDERMIS bounded on the inside by a BASEMENT MEMBRANE and on the Detect movements, vibrations, outside by the CUTICLE other mechanical disturbances TOUCH – monitored by hair sensilla, - epicuticle innervated by a single neuron - exocuticle - endocuticle HEARING - perception of aerial  to enzymes that breakdown parts of ------------------ CUTICLE the old cuticle before it is shed ------------------ EPIDERMIS When first laid on the surface, it is deeply folded and later, straighten after ecdysis ------------------ BASEMENT MEMBRANE (insect swallow air) Layers: Homogenous layer - innermost layer Layers of cuticulin (lipoprotein) = critical in the growth process Wax ( long hydrocarbon chain) Cement ( tanned protein with lipids serving as a varnish-like covering of the wax or maybe in the form of an open meshwork providing a reservoir of lipids to replace lost surface lipids) INTEGUMENTARY SYSTEM LAYERS OF THE CUTICLE - The CUTICLE EXOCUTICLE Produced by the epidermis Thicker layer Covers the entire body surface = Forms the exuvium at molting restricts water loss Gives the cuticle its characteristic Lines the insect’s air tubes, salivary strength and resilience glands, and parts of the alimentary tract (fore- & hindgut) Formed of chitin (C18H13NO5) complexed with protein PRIMARY LAYERS OF THE CUTICLE Chitin is a polymerized compound, a EPICUTICLE nitrogenous polysaccharide linked to a protein. This is common in nature the thin outer layer, 3 mµ to 0.1 mµ as a base for materials like wood, thick; permeable to chemicals and hair, horn nutrients for growth but impermeable ENDOCUTICLE  Still a thicker layer Bristles/chaetae = large setae Basement membrane composed of mucopolysaccharide Scales on Lepidoptera are flattened secreted by hemocytes. Along it run setae the nerves, tracheoles 3 separate cells form each seta The integument of an insect 1. Trichogen cell = for hair formation 2. Tormogen cell = for socket formation 3. Sensory cell INTEGUMENTARY SYSTEM PORE CANALS are passageways of secretions by the epidermis from inside to outside. Epidermal secretions make possible the repair of the cuticle, INTEGUMENTARY SYSTEM secretion of wax and release tanning agents. CUTICULAR EXTENSIONS ❖ [THE INSECT STRUCTURES ARE 1. SPINES - multicellular with FORMED FROM THE BODY undifferentiated epidermal cells WALL], 2. SETAE OR HAIRS OR ❖ THE BODY WALL SUPPLIES A MACROTRICHIA OR TRICHOID SUPPORT SYSTEM KNOWN AS SENSILLA - multicellular with EXOSKELETON specialized cells Functions of the exoskeleton 3. ACANTHAE that are unicellular in origin 1. Provides a rigid foundation for the body 4. MICROTRICHIA - subcellular, from several to many extensions per cell 2. Serves as a point of attachment of muscles SETAE sense much of the insect’s 3. Serves as a covering to protect tactile environment internal organs  SECRETE A SPECIAL LIPOPROTEIN 4. Helps prevent desiccation (CUTICULIN MOLTING LAYER) THAT INSULATES AND E.g, Cicada (nymph), order (Homoptera) PROTECTS THE EC FROM MOLTING FLUID’S (MF) DIGESTIVE ACTION. THE EXUVIAE CUTICULIN LAYER BECOMES PART OF - Molted “skin” / Exoskeleton THE NEW EXOSKELETON’S EPICUTICLE MOLTING (casting of the old cuticle) IS MOLTING TRIGGERED BY HORMONES RELEASED WHEN AN INSECT’s GROWTH REACHES 4. Activation of molting fluid the PHYSICAL LIMITS OF ITS EXOSKELETON AFTER THE FORMATION OF THE CUTICULIN LAYER, MF BECOMES What happens during molting? ACTIVATED AND CHEMICALLY PHYSIOLOGY OF MOLTING/DISTINCT “DIGESTS” THE ENDOCUTICLE OF THE SEQUENCE OF EVENTS OLD EXOSKELETON. 2 processes : MOLTING Apolysis – cuticle separates from the 5. Absorption of the digested remains of old epidermis cuticle and start of secretion of new procuticle Ecdysis - shedding off of the old skin BREAKDOWN PRODUCTS (AA AND 1. Changes in epidermal cells CHITIN MICROFIBRILS) PASS THRU THE CUTICULIN LAYER WHERE THEY ARE EPIDERMAL CELLS RESPOND TO RECYCLED BY THE EPIDERMAL CELLS HORMONAL CHANGES BY INCREASING AND SECRETED UNDER THE CUTICULIN THE RATE OF PROTEIN SYNTHESIS LAYER AS A NEW PROCUTICLE =EXO THAT QUICKLY LEADING TO APOLYSIS AND ENDOCUTICLE (SOFT AND (physical separation of epidermis from old WRINKLED) endocuticle) 6. Formation of wax and cement layer MOLTING Wax line the pore canals for water retention 2. Secretion of molting fluid and water loss mechanism EPIDERMAL CELLS (EC) FILL THE PORE CANALS WITHIN THE RESULTING GAP WITH AN INACTIVE PROCUTICLE ALLOW MOVEMENT OF MOLTING FLUID LIPIDS AND PROTEIN TOWARD THE NEW EPICUTICLE WHERE WAX AND 3. Secretion of cuticulin layer CEMENT LAYER FORM. 7. Ecdysis and expansion of the new cuticle 1. Changes in epidermal cells WHEN THE NEW EXOSKELETON IS READY, MUSCULAR CONTRACTIONS 2. Secretion of molting fluid AND INTAKE OF AIR CAUSE THE 3. Secretion of outer layer of cuticulin INSECT’S BODY TO SWELL AND THE 4. Secretion of homogenous layer of OLD E SPLITS OPEN ALONG LINES OF cuticulin WEAKNESS (ECDYSIAL SUTURES) AND 5. Activation of molting fluid THE INSECT SHEDS OLD SKIN QUICKLY 6. Absorption of the digested remains (ECDYSIS) AND CONTINUES TO FULLY of old cuticle EXPAND THE NEW ONE. 7. Start of secretion of new procuticle (exo/endocuticle) 8. Sclerotization /Tanning 8. Ecdysis and expansion of the new –processes by which the new cuticle is cuticle made more resistant to degradation, stiffer, 9. Sclerotization less soluble. Processes by which cuticular 10. Start of wax secretion proteins are cross-linked by the action of quinones, and therefore change the cuticle into dark, hard, insoluble material. CONTROL OF MOLTING AND QUINONES= tanning subset for the cuticle ASSOCIATED PROCESSES coming from tyrosine or para-OH phenylalanine in the hemolymph 1. Ecdysone – plays a vital role in controlling the events of molting; triggers the ❖ Β – sclerotization = for hardening epidermal cells to change without development of new color (MOLTING HORMONE) ❖ Quinone sclerotization = hardening with colors 2.Bursicon – controls sclerotization = necessary for cuticle tanning and 9. Start of wax secretion endocuticle formation in flies WAX STARTS TO BE SECRETED 3. A hormone released from the corpora allata-corpora cardiaca complex with PHARATE CONDITION = INSECT ecdysone to control wax secretion. ACTIVELY CONSTRUCTING NEW EXOSKELETON TAKES DAYS OR continuation: Control WEEKS TENERAL CONDITION = NEWLY 4. A hormone with ecdysone controlling MOLTED INSECT, SOFT endocuticle production UNPIGMENTED (WHITE OR IVORY), 5. Ecdepteroids induce sclerotization in ligated abdomen of blowfly larvae resulting PHYSIOLOGY OF MOLTING/DISTINCT to the induction of de novo synthesis of SEQUENCE OF EVENTS enzyme dopa-decarboxylase in the epidermal cells DIFFERENT TYPES OF CUTICLE 10. REPRODUCTIVE SYSTEM The cuticle varies in nature in the different COMPOSITION parts of the insect’s body Male’s testes = sperm 1. RIGID CUTICLE Female’s ovaries = eggs (ova) Produced as a result of tanning in the outer part of the procuticle to forming an MODE OF REPRODUCTION IN INSECTS exocuticle, but the extent of tanning, and hence the hardness of the cuticle varies 1. Sexual 2. Asexual e.g. nymphs of Schistocerca 3. Sexual and asexual for some (grasshopper) insects 2. MEMBRANOUS CUTICLE MALE’S REPRODUCTIVE SYSTEM Flexible arthrodial membranes join the Pair of testes located near back of sclerites and in these, the procuticle abdomen.Subdivided into several remains untanned hundred follicles (sac-like tubes) where sperms are produced e.g. Membrane between 2 adjacent sclerites resulting to unrestricted Spermatogonia – a group of germ movement cells at the distal end of each follicle, dividing thru mitosis and increase in 3. ELASTIC AND EXTENSIBLE size to form spermatocytes CUTICLE Spermatocytes – migrate toward the Some parts of the cuticle contain a end of the follicle, push along by colorless, rubber-like protein called continued cell division of resilin spermatogonia; undergo meosis: 4 haploid spermatids 🡪 mature e.g. those found in elastic hinges such as spermatozoa wing-hinge ligament lying between the pleural process and the 2nd maxillary Vasa efferentia – where mature sclerite sperm from the testes pass out Seminal vesicle (storage chamber) – where mature sperms collect  Vasa deferentia - join one another produced regularly within each ovariole near midline to form a single during active oogenesis (egg maturation) ejaculatory duct Ejaculatory duct - where sperm passes out of the males body thru a Oocytes copulatory organ called aedeagus Egg cells differentiated from the Accessory glands oogonium, before maturation - 1 or more pairs of secretory glands; in Periplaneta, form dense bunches Migrate toward the basal end of of tubules called the “mushroom ovariole, pushed along by continued gland” of Huxley cell division of oogonia Functions: Undergo meiosis: yields 4 cells, 1 egg, and 3 polar bodies which 1. Manufacture of seminal fluid that disintegrate or may accompany the sustains and nourishes mature egg as nurse cells sperm while in the male’s genitalia (vitellogenesis = deposition of 2. Produce spermatophores, yolk in the oocyte) proteinaceous pouch-like structures that encase sperm, base of ovariole (calyx) FEMALE’S REPRODUCTIVE SYSTEM common oviduct opening into a genital chamber (BURSA COPULATRIX) or Pair of ovaries copulatory pouch Swell with developing eggs when Female accessory glands insect is actively reproducing, nearly filling the abdomen 1 or more pairs; usually connected by small ducts to common oviduct or Each is subdivided into ovarioles bursa copulatrix (dozens aligned parallel to one another) where eggs are actually supply lubricants for the system produced Secrete protein-rich eggshell Oogonia (the first stage in the (chorion) that surrounds the egg differentiation of an egg cell) A group of germ cells near the distal end of ❖ Copulation (male deposits each ovariole, dividing through mitosis, spermatophore in bursa increase in size to form oocytes which are copulatrix  ❖ Peristaltic contraction force form and size until it reaches spermatophore into female’s adulthood. spermatheca (pouch-like, for storage of sperm for weeks, months, even years) The spermathecal gland produce: ATYPICAL MODES OF REPRODUCTION Enzymes to digest the protein coat of spermatophore 1. Parthenogenesis - Definition: Development from an Nutrients to sustain sperm in storage unfertilized egg. - Types: - Thelytokous Parthenogenesis REPRODUCTIVE SYTEM - Females produce only female offspring. Ovulation takes place - Examples: Certain species of Diptera (flies) and Coleoptera (beetles). Eggs go to spermatheca and stimulate the release of a few sperm - Arrhenotokous Parthenogenesis onto the egg’s surface - Females produce only male offspring. - Examples: Hymenoptera (bees, ants, Sperm swim through a wasps), scale insects, and whiteflies. special opening in the eggshell - Amphitokous or Deuterotokous called the micropyle, Parthenogenesis - Females produce both male and oviposition or egg–laying follows female offspring. closely - Examples: Thysanoptera (thrips, which can undergo all types of egg begins embryonic development parthenogenesis), aphids, and some species of wasps. Phases of Insect Development Types of Paedogenesis 1. Embryonic Development ○ Occurs within the egg after 1. Larval Paedogenesis fertilization. ○ Description: Production of ○ Involves the formation and offspring by a larval stage. growth of the insect embryo. ○ Example: Gall midges 2. Post-Embryonic Development (Family: Cecidomyiidae). ○ Begins once the egg 2. Pupal Paedogenesis hatches. ○ Description: Embryos are ○ Involves metamorphosis, formed within the where the insect changes in haemocoele (body cavity) of a paedogenetic mother pupa  (also known as a hemi- Male Emergence: pupa). ○ Occasional males arise from unfertilized eggs. NEOTENY ○ These males are apparently functional and can contribute Definition: A phenomenon where a to the reproduction process. non-terminal instar (juvenile stage) Fertilized Eggs: develops reproductive features ○ These develop from females typical of an adult. This includes and are essential for abilities such as: population growth in ○ Locating a mate hermaphroditic species. ○ Copulating ○ Depositing eggs or larvae in Reproductive Strategies: "To Lay Eggs a typical manner or Not to Lay Eggs" ○ Example Organisms: 1. Oviparity ○ Scale Insects: Exhibit neotenous development, Definition: Fertilized eggs are laid allowing juvenile stages to outside the mother's body. reproduce. ○ Strepsiptera (Twisted-Wing 2. Ovoviviparity Parasites): ○ Female development stops Definition: Fertilized eggs are at the puparium stage, retained within the mother's body meaning they do not until they are ready to hatch. progress to a fully mature adult form yet retain 3. Viviparity reproductive capabilities. Definition: Embryos develop inside ATYPICAL MODE OF REPRODUCTION the mother's body and receive direct nourishment from her. 1. Hermaphroditism Definition: Hermaphroditism is a condition where individuals possess B. CORPORA ALLATA (CA) both male (testes) and female (ovaries) reproductive organs. Overview Ovotestis: An organ that contains both testicular and ovarian tissue. Structure: A pair of small, ovoid ○ Example: Cottony cushion cellular bodies scale (Icerya purchasi) Origin: Ectodermal Location: Associated with the 2. Reproductive Process in stomodaeal ganglion behind the Hermaphroditic Species brain Function Supply: Rich tracheal and often nerve supply Primary Role: Produce juvenile hormone (JH) Function: Juvenile Hormone (JH) Functions Hormone Production: Produce ecdysone (molting hormone) 1. Metamorphosis Control ○ Regulates the process of Ecdysone (Molting Hormone) metamorphosis in insects. 2. Reproductive Development Role in Insects: Regulation ○ Induces immature insects to ○ Influences the synthesis of molt. yolk precursors ○ Initiates the tanning process (vitellogenins). during molting. ○ Regulates yolk deposition in ○ Required for egg production. eggs. Lifecycle Dynamics: 3. Antagonism to Ecdysone ○ Breaks down or degenerates ○ Counteracts the effects of soon after the final molt to ecdysone on spermatogonial adulthood. division. ○ Exceptions: 4. Inhibition of Adult Characteristics Thysanura: Molting ○ Delays the appearance of continues after sexual adult traits in developing maturity. insects. Solitary Locusts: 5. Molting Process Continue to molt as ○ Ensures normal development well. during molting, induced by Interactions with Other thoracic gland hormones, Hormones: resulting in the correct ○ Antagonizes the effect of sequence of nymphal or vitellogenesis, which is larval instars. stimulated by juvenile hormone. C. Thoracic/Prothoracic Glands Overview: Other Hormones Thoracic or prothoracic glands are a 1. Anterior Segment Refraction pair of diffused glands located at the Factor (ARF) back of the head or in the thorax. Source: Cerebral neurosecretions Anatomy: released from peripheral nerve endings. Location: Back of the head or Functions: thorax ○ Involved in pupariation.  ○ Aids in the production of DOPA (di-hydroxy phenyl alanine) through the action of decarboxylase. 2. Puparium Tanning Factor (PTF) Source: Also released from peripheral nerve endings. Functions: ○ Plays a role in pupariation. ○ Regulates the synthesis of enzymes at the transcriptional level, essential for the hydroxylation of tyrosine. DEFINITION OF TERMS ABSORPTION – process by which a chemical crosses the various membrane barriers of a living organism and especially those processes by which a chemical is taken up from environmental media, including food and other ingested material. Toxicity Overview Definition: Toxicity refers to the ability of a poison (e.g., pesticide) to produce adverse effects, which can range from mild symptoms like headaches to severe outcomes such as coma, convulsions, or death. It is the capacity of a substance to cause injury and is a measurable quantity.