Lec. 14 Metamrphsis and types, diapause in insect.ppt
- 1. 1 R.K. Panse Asstt. Prof. (Entomology) Lecture no. 14 METAMRPHSIS AND INSECT DIAPAUSE
- 2. 2 Metamorphosis Metamorphosis is when species of insects and animals hatch from a fertilized egg, go through a series of changes in body form to become adults. There are five kinds of metamorphosis 1. Ametamorphosis 2. Incomplete Metamorphosis 3. Complete Metamorphosis 4. Intermediate metamorphosis 5. Hyer metamorphosis
- 3. 3 Insects do not undergo any metamorphosis. When the insect hatches from the egg, it resembles the adult in all the characters except the small body size, which later increases, until they reach sexual maturity with well developed reproductive organs. e.g.: Apterygotes e.g.: silver fish, springtails. Ametamorphosis
- 4. 4 Incomplete Metamorphosis Life completed in three stages: -Egg -Nymph -Adult Fertilized egg hatches into a nymph that looks like a small adult but does not have wings. The nymph molts several times before reaching the adult stage. Insect goes through various stages of molting and growing but remain basically the same. Young grows bigger and bigger but has same feeding habits and physical appearance Examples are: praying mantis, crickets and grasshoppers
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- 6. 6 Complete Metamorphosis Four stages of development -eggs -larva -pupa -adult A fertilized egg hatches into worm- like larva stage. During this time it eats and grows before forming a shelter called a cocoon or chrysalis. Then goes into a resting stage called the pupa.
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- 8. 8 4. Intermediate metamorphosis In this case, insects may undergo either hemi or holometamorphosis. If they undergo holometamorphosis, there is a short pupal stage. e.g.: coccids, thrips etc. 5. Hypermetamorphosis This is a peculiar type of development which consists of two or more types or forms of larvae in the life cycle of insects. In majority of the cases the first larval instar is campodeiform and the subsequent larval forms depends on type and mode of life of the larva. E.g.: In blister beetle (Meloidae; Coleoptera), the first larval instar is campodeiform followed by scarabeiform larval type.
- 9. 9 Ametabola (No metamorphosis) Hemimetabola (Incomplete metamorphosis) Holometabola (Complete metamorphosis) Wingless Wings develop during growth of young one (nymph) Wings develop during growth of adult inside pupae Undergo slight or no metamorphosis Undergo incomplete metamorphosis Undergo complete Metamorphosis Life cycle includes 3 developmental stages: egg, larva (many) and adult Life cycle includes 3 developmental stages: egg, nymph and adult Life cycle includes 4 developmental stages: egg, larva, pupa and adult Eggs laid with no coverings Eggs are often covered by an egg case Eggs are sometimes covered by hairs/scales No changes take place during development Young one (immature stage) is called nymph. Young one (immature stage) is called as larvae. The development is direct (young one to adult) The development is direct (young one to adult) The development is indirect (youngone to pupa, then to adult) Differences between 3 major types of metamorphosis:
- 10. 10 Ametabola (No metamorphosis) Hemimetabola (Incomplete metamorphosis) Holometabola (Complete metamorphosis) Young (immature) looks like the adult in all characters, only it may be missing sexual organs Young one (nymph) resembles the adult in all characters except in wings Young one (larva) does not resemble and differs from adult both in morphological characters & feeding habits. Larva/Nymph directly becomes adult Nymph directly becomes adult Young one undergo pupal stage before adult stage No pupal stages Pupal stage absent Pupal stage present All Apterygote insects Characteristics of lower insect orders : Exopterygote insects Characteristic of higher orders: Endopterygote insects
- 11. 11 It is the period of arrested growth or development in the life cycle of the insects during which the physiological processes like differentiation and reproduction are suspended. Diapause is represented by low rate of metabolism, low O2 consumption, low body weight, low body water content and vitamin deficiency in the blood. Diapause may occur in egg, larva, nymph, pupa or adult stage. For example: Egg diapause – Silk worm Larval diapause- Pink boll worm Pupal diapause- Red hairy Caterpillar Adult diapause- Mango nut weevil INSECT DIAPAUSE
- 12. 12 Diapause is of two types: 1. Obligatory diapause: It refers to the stage of suspended activity of the insect which is a hereditary character controlled by genes and is species specific. e.g. egg diapause in silkworm 2. Facultative diapause: It is the stage of suspended activity of the insect due to unfavourable conditions and with the onset of favourable condition, the insect regains its original activity. e.g. Cotton pink bollworm Pectinophora gossypiella. The occurrence of diapause during summer due to high temperatures is known as “aestivation” where as the period of inactivity during winter due to low temperatures known as “hibernation”.