Pra embryonic and post-embryonic development in insect

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Pra embryonic and post-embryonic development in insect

  1. 1. Pra-embryonic and Post-embryonic Development in Insect
  2. 2. Outline • Pre-embryonic Development • Embryonic Development • Post-embryonic Development
  3. 3. Pre-embryonic Fertilization • 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 to form a diploid zygote -- a one-celled embryo. • This event is known as fertilization. • After the egg is fertilized, it undergoes a period of rapid growth and development known as embryogenesis.
  4. 4. • The micropyle, a special opening near the anterior end of the chorion, serves as a gateway for entry of sperm during fertilization.
  5. 5. • A female receives sperm from her male partner during the act of mating---insemination • 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.
  6. 6. Embryonic Development
  7. 7. Egg  In most insects, life begins as an independent egg.  This type of reproduction is known as oviparity.  Manufactured within the female's genital system  Released from her body through an ovipositor  Production of eggs by the female is called oogenesis  The egg-laying process is known as oviposition.
  8. 8. • Each insect species produces eggs that are genetically unique and often physically distinctive as well -- spherical, ovate, conical, sausage-shaped, barrel-shaped, or torpedo-shaped. • Each egg is composed of only a single living cell -- the female gamete.
  9. 9. Some types of eggs
  10. 10. Egg structure • Egg shell-chorion • Vitelline membrane • Periplasm • Nucleus • Micropyle • Yolk • Cytoplasm • Cytoplasm reticulum chorion Vitelline membrane Periplasm
  11. 11. • The egg is covered by a protective "shell" of protein secreted before oviposition by accessory glands in the female's reproductive system. • This egg shell, called the chorion , is sculptured with microscopic grooves or ridges that may be visible only under an electron microscope. • The chorion is perforated by microscopic pores (called aeropyles ) that allow respiratory exchange of oxygen and carbon dioxide with relatively little loss of water. chorion
  12. 12. Oviparous- expulsion of egg from oviduct Ovoviviparous- eggs incubated in reproductive tract hatch immediately upon being laid Viviparous- Giving birth to young. Several forms of this are seen in insects. Egg Fertilization Egg Egg Fertilization Fertilization Egg membrane Placental (aphids), haemocoelus (hemocoel, gall midges), adentrophic (nurse gland, fully grown larva tsetse fly. The main type of Reproduction
  13. 13. The Other Type of Reproduction In Insect • Paedogenesis – Reproduction by larval insects • Parthenogenesis – Development without fertilization – Unfertilized eggs produce: • Males (arrhenotoky) in Hymenoptera • Females (thelytoky) • Both (amphitoky) in aphids, some wasps • Polyembryony
  14. 14. Polyembryonic • Found in some endoparasitic groups only • Single egg results in 2 to ‘several thousand’ larvae • Some larvae may be ‘defender morphs’ – Hatch more quickly – Eliminate rival parasites – Fail to pupate & they die • Remaining larvae become ‘reproductive morphs’ that complete development and reproduce to carry on the species
  15. 15. EMBRYONIC PROCESS  A developmental process that usually begins once the egg has been fertilized.  It involves multiplication of cells (by mitosis) and their subsequent growth, movement, and differentiation into all the tissues and organs of a living insect.
  16. 16. Embryonic Development
  17. 17. Developmental Fate of Insect Germ Layers • Ectoderm: Epidermis, exocrine glands, brain and nervous system, sense organs, foregut and hindgut, respiratory system, external genitalia. • Mesoderm: Heart, blood, circulatory system, muscles, endocrine glands, fat body, gonads • Endoderm: Midgut.
  18. 18. Embryonic development of tobacco hornworm M. sexta egg showing micropyle .Manduca sexta eggs. M. sexta embryo 19 hours after fertilization M. sexta embryo 37 hours after fertilization M. sexta embryo 57 hours after fertilization M. sexta embryo 115 hours after fertilization. Newly emerged larva showing the head
  19. 19. Summary of Insect Development Yolk distribution- centralized Cleavage type - meroblastic, only portion of yolk undergoes cleavage Blastula- steroblastic Gastrulation- ingression and invagination Blastospore type- protostome (mouth and anus from blastospore) Larval development- multiple molts, maggot, nymph, caterpillar, pupa, adult (imago) Developmental determination- mosaic pattern
  20. 20. POST-EMBRYONIC DEVELOPMENT
  21. 21. • Once the hatching emerges, it is called a first instar nymph (or larva). • As it grows, it will continue to develop and mature. • These post-embryonic changes are known as morphogenesis.
  22. 22. 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 replace its exoskeleton (a process known as molting).
  23. 23. • 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). • Collectively, all changes that involve growth, molting, and maturation are known as morphogenesis.
  24. 24. Timeline of MORPHOGENESIS Instar
  25. 25. Molting • The molting process is triggered by hormones released when an insect's growth reaches the physical limits of its exoskeleton. • Each molt represents the end of one growth stage (instar) and the beginning of another
  26. 26. • In some insect species the number of instars is constant (typically from 3 to 15), but in others it may vary in response to temperature, food availability, or other environmental factors. • Molting stops when the insect becomes an adult -- energy for growth is then channeled into production of eggs and sperm.
  27. 27. • An insect cannot survive without the support and protection of its exoskeleton, so a new, larger replacement must be constructed inside the old one -- much like putting an overcoat under a sweater!
  28. 28. • An insect that is actively constructing new exoskeleton is said to be in a pharate condition. • During the days or weeks of this process there may be very little evidence of change. • Ecdysis, however, occurs quickly (in minutes to hours).
  29. 29. • A newly molted insect is soft and largely unpigmented (white or ivory). • It is said to be in a teneral condition until the process of tanning is completed (usually a day or two).
  30. 30. 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
  31. 31. Exoskeleton traits • fixed in size • new exoskeleton  Incorporates the changes that are part of metamorphosis.  Initially soft and is larger than the old exoskeleton.
  32. 32. • Stages between each molt are called instars.  first stage which emerged from the egg is the first instar or nymph. -- to grow must shed its skin or molt -- may be four or five instars before the adult stage is reached
  33. 33. Cicada Ecdysis An adult cicada (Homoptera) just after molting
  34. 34. Thank You

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