Insect Development and Growth PDF

Topic 4: Insect Development and Growth  Outline Introduction Life History Patterns & Structures Egg Structure Embryogenesis Morphogenesis  Introduction Insect has various growth phases: egg, immature development, emergence of a...

Topic 4: Insect Development and Growth  Outline Introduction Life History Patterns & Structures Egg Structure Embryogenesis Morphogenesis  Introduction Insect has various growth phases: egg, immature development, emergence of adult. Insect growth is discontinuous - sclerotized cuticular parts of the body. Size increase is by molting (the periodic formation of new cuticle of greater surface area); and subsequent ecdysis (shedding of the old cuticle)  Life History Patterns & Structures Growth is an important part of an individual’s ontogeny (the developmental history of the organism from egg to adult). Changes in morphology during ontogeny affect both external & internal organs. Metamorphosis in insects is the biological process of development all insects must undergo. There are two forms of metamorphosis: incomplete metamorphosis and complete metamorphosis.  Types of metamorphosis: - Ametabolous: no metamorphosis - Hemimetabolous: incomplete - Holometabolous: complete Ametabolous: - PrimiLve developmental paMern - Retained by the primiLve wingless orders (Archaegnatha-bristletails; Zygentoma-silverfish) - Apterygota - Emerge from the egg in a form essenLally resembling a miniature adult, lacking only genitalia - Immatures are called young  Hemimetabolism: - Incomplete metamorphosis (also called Exopterygota) - Growth from one nymph stage to the next occurs by molting - An insect molts when it outgrows its exoskeleton, which does not stretch and would otherwise restrict the insect's growth. - The molting process begins as the insect's epidermis secretes a new epicuticle - A nymph's wings get larger with each successive shedding of skin, and by maturity as an adult, the wings are fully developed.  Immature insects that go through incomplete metamorphosis are called nymphs or in the case of dragonflies and damselflies as naiads. Nymphs are similar in form to the adult except for the presence of wings, which are not developed until adulthood. The life cycle of a hemimetabolous insect, the southern green stink bug or green vegetable bug, Nezara viridula (Hemiptera: Pentatomidae), showing the eggs, nymphs of the five instars, and the adult bug on a tomato plant. This cosmopolitan and polyphagous bug is an important world pest of food and fiber crops. (After Hely et al. 1982.) The mayfly > pollution–sensitive animals. This means if mayflies are in or around the water, the water should be of a good quality.  Holometabolous: - Complete metamorphosis - Insect changes all in four stages, an egg or embryo, a larva, a pupa, and the adult or imago. - Most successful insect groups, such Endopterygota, use a system of complete metamorphosis Schematic drawing of the life cycle of a non-biting midge (Diptera: Chironomidae, Chironomus) showing the various events and stages of insect development.  In-vitro Rearing and Growth Development of Heterotrigona itama 1.6x magnification A B C D ̴Day 1-3: egg ̴Day 2-3: larvae ̴Day 3-5: larvae ̴Day 5-7: larvae E F G H ̴Day 7-9: larvae ̴Day 9-20: larvae ̴Day 20-50: pupae Adult A) ̴ 1 to 2 day old egg; B) ̴ 2 to 3 day old larvae; C) ̴ 3 to 5 day old larvae; D) ̴ 5 to 7 day old larvae; E) ̴ 7-9 day old larvae; F) ̴ 9 to 20 day old larvae; G) ̴ 20-50 day old pupae; H) ̴ Adult of Heterotrigona itama (Queen)  Egg Structure In most insects, life begins as an independent egg. This type of reproducLon is known as oviparity. Each egg is manufactured within the female's genital system and is eventually released from her body through an ovipositor, a tube-like, saw-like, or blade- like component of her external genitalia. ProducLon of eggs by the female's body is called öogenesis and the egg-laying process is known as oviposiLon.  Each insect species produces eggs that are gene?cally unique and oBen physically dis?nc?ve as well -- spherical, ovate, conical, sausage-shaped, barrel-shaped, or torpedo- shaped. micropyle vitelline membrane nuclues yolk cytoplasmic reticulum Eggs of chorion aeropyles Rhynchophorus ferrugineus  How fer(liza(on occurs in insects? A female receives sperm from her male partner during the act of mating. She can store that sperm for long periods of time in a special part of her reproductive system, the spermatheca. As a developing egg moves past the opening to the spermatheca, a few sperm are released onto its surface. The sperm swim toward the micropyle -- the first one to reach its destination enters and injects its nucleus into the egg. The sperm nucleus quickly fuses with the egg nucleus (syngamy) to form a diploid zygote -- a one-celled embryo. This event is known as fertilization. This slide will be further discussed during our synchronize lecture (Webex mee9ng)  Embryogenesis Embryogenesis is a developmental process that usually begins once the egg has been ferLlized. It involves mulLplicaLon of cells (by mitosis) and their subsequent growth, movement, and differenLaLon into all the Lssues and organs of a living insect. An insect's egg is much too large and full of yolk to simply divide in half like a human egg during its iniLal stages of development  Mouth opening Developmental Fate of Insect Germ Layers Ectoderm: Epidermis, exocrine glands, brain and nervous system, Labrum sense organs, foregut and Antennae hindgut, respiratory system, Mandibles, maxillae, external genitalia. labium Legs Mesoderm: Heart, blood, circulatory Abdomen system, muscles, endocrine glands, fat body, gonads (ovaries and testes). Embryonic development of appendages: Midgut. Endoderm: -Mouth opening -Labrum -Antennae -Mandibles, maxillae, labium -Legs -Abdomen -Intercalaries  In general, the rate of embryonic development depends on temperature (insects are poikilothermic) and on species-specific characteristics of development. Embryogenesis ends when the yolk's contents have been consumed: the immature insect is fully formed and ready to hatch from the egg. As it grows, it will continue to develop and mature. These post-embryonic changes are known as morphogenesis.  Morphogenesis Once an insect hatches from the egg it is usually able to survive on its own, but it is small, wingless, and sexually immature. Its primary role in life is to eat and grow. If it survives, it will periodically outgrow and replace its exoskeleton (a process known as molLng). In many species, there are other physical changes that also occur as the insect gets older (growth of wings and development of external genitalia, for example). CollecLvely, all changes that involve growth, molLng, and maturaLon are known as morphogenesis.  Summary of Molting Step 1: Apolysis -- separation of old exoskeleton from epidermis Step 2: Secretion of inactive molting fluid by epidermis Step 3: Production of cuticulin layer for new exoskeleton Step 4: Activation of molting fluid Step 5: Digestion and absorption of old endocuticle Step 6: Epidermis secretes new procuticle Step 7: Ecdysis -- shedding the old exo- and epicuticle Step 8: Expansion of new integument Step 9: Tanning -- sclerotization of new exocuticle The nymphal–imaginal molt of a male dragonfly of Aeshna cyanea (Odonata: Aeshnidae). The final-instar nymph climbs out of the water prior to the shedding of its cuticle. The old cuticle splits mid-dorsally, the teneral adult frees itself, swallows air, and must wait many hours for its wings to expand and dry. (After Blaney 1976.)  Ictinogompus rapax Paragomphus caprinicornis Tholymis tillarga Macromidia shanensis  Most larvae can be grouped into one of five categories based on physical appearance: Common Larval Type Description Examples Name Body cylindrical with short Moths and Eruciform Caterpillar thoracic legs and 2-10 pairs of butterflies fleshy abdominal prolegs Elongated, flattened body with Lady beetle, Campodeiform Crawler prominent antennae and/or cerci. lacewing Thoracic legs adapted for running Body robust and "C"-shaped with June beetle, Scarabaeiform White grub no abdominal prolegs and short dung beetle thoracic legs Body long, smooth, and cylindrical Click beetle, Elateriform Wireworm with hard exoskeleton and very Flour beetle short thoracic legs Body fleshy, worm-like. No head House fly, flesh Vermiform Maggot capsule or walking legs fly Examples of larval types. Polypod larvae: (a) Lepidoptera: Sphingidae; (b) Lepidoptera: Geometridae; (c) Hymenoptera: Diprionidae. Oligopod larvae: (d) Neuroptera: Osmylidae; (e) Coleoptera: Carabidae; (f) Coleoptera: Scarabaeidae. Apod larvae: (g) Coleoptera: Scolytinae; (h) Diptera: Calliphoridae; (i) Hymenoptera: Vespidae. ((a,e–g) After Chu 1949; (b,c) after Borror et al. 1989; (h) after Ferrar 1987; (i) after CSIRO 1970.)  Pupae can be grouped into one of three categories based on physical appearance: Common Pupal Type Description Examples Name Developing appendages (antennae, wings, legs, etc.) held tightly Butterflies and Obtect Chrysalis against the body by a shell-like moths casing. Often found enclosed within a silken cocoon. All developing appendages free and Exarate None Beetles, Lacewings visible externally Body encased within the hard Coarctate Puparium exoskeleton of the next-to-last Flies larval instar Examples of pupal types. Exarate decticous pupae: (a) Megaloptera: Sialidae; (b) Mecoptera: Bittacidae. Exarate adecticous pupae: (c) Coleoptera: Dermestidae; (d) Hymenoptera: Vespidae; (e,f ) Diptera: Calliphoridae, puparium and pupa within. Obtect adecticous pupae: (g) Lepidoptera: Cossidae; (h) Lepidoptera: Saturniidae; (i) Lepidoptera: Papilionidae, chrysalis; (j) Coleoptera: Coccinellidae. ((a) After Evans 1978; (b,c,e,g) after CSIRO 1970; (d) after Chu 1949; (h) after Common 1990; (i) after Common & Waterhouse 1972; (j) after Palmer 1914.)  Review Introduction Life History Patterns & Structures Egg Structure Embryogenesis Morphogenesis