3. hermaphrodite 4. parthenogenesis. 5. Spermatophore 6. spermatheca 7. ovipary

Question

3. hermaphrodite 4. parthenogenesis. 5. Spermatophore 6. spermatheca 7. ovipary 8. ovovivipary 9. vivipary 10. naiad What is direct development and in which insect orders can this be found? Describe or illustrate the ontogenetic stages (lifecycle) of a hemimetabolic (gradual metamorphosis) insect. Describe point by point/or illustrate the ontogenetic stages that are found in holometabolic (complete metamorphosis) insects and also name the function (role) of each stage. Explain to what degree the terms apterygota, exopterygota. paieoptera, neoptera and endopterygota relate to metamorphosis and how this is accounted for in the classification of the insect orders. Describe hormonal control of metamorphosis in insects and specifically indicate the endocrine g as well as the hormones that are involved and their target/function. What is diapause and what is the adaptive value thereof?

Explanation / Answer

Apterygota is a subclass of insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history. The nymphs go through little or no metamorphosis, they look like as adult. The apterygotes are a primitive group of insects that diverged from other ancient orders before wings evolved. Apterygotes have a number of other primitive features not shared with other insects. When egg hatched, the young closely resemble adults and do not undergo any metamorphosis, and lack even an identifiable nymphal stage. They continue to molt throughout life, undergoing multiple instars after reached at sexual maturity, whereas all other insects undergo only a single instar when sexually mature. A typical apterygote, for example, is wingless and has six legs. The presence of six legs was once an important feature in the identification of true insects of the apterygotes. e.g. Silver fish.

The Exopterygota are a super order of insects of the subclass Pterygota in which the young resemble adults but have externally developing wings. They undergo a modest change between immature and adult, without going through a pupal stage. The nymphs develop gradually into adults through a process of moulting. The Exopterygota life cycle includes egg, larva or nymph and end at adult . The transformation from larva to adult is gradual and proceeds by moulting. The wings development takes place externally, So this group if insect is called Exopterygota. The Exopterygota differ from the Endopterygota in that they generally undergo an incomplete metamorphosis. Their life cycle typically lacks a clearly defined pupal phase. In winged species the nymphs generally bear external wing. e.g. dragonflies grasshoppers, cockroach, crickets, aphids, bugs etc.

Endopterygota is a superorder of insects with distinctive larval, pupal, and adult stages. They undergo a radical metamorphosis, with the larval and adult stages differing significantly in their structure and behaviour. They show complete metamorphism. Wing pads develop internally so; this group of insects is called as Endopterygota. Transformation into adults the larva has to pass with a resisting phase called pupa. Feeding and movement ceases and metabolic activities are lowered down during the pupal stage but conspicuous changes in morphological forms in the development of wings and reproductive organs occur in the pupal stage. This is specialized type of metamorphosis found in higher orders of Endopterygota insects. It is a type of complete metamorphosis in which different larval instars represent two or more markedly different types of larvae. The first instars larva is active and the subsequent larval instars are vermiform. e.g. blister beetles.

Paleopteran is the most primitive winged insects have large, membranous wings that are held continuously out to the side of the body or over the back of the thorax. These insects do not have the ability to fold their wings down flat over the abdomen. This primitive condition are grouped as Paleoptera, within the subclass Pterygota. The name Palaeoptera has been traditionally applied to those ancestral groups of winged insects that lacked the ability to fold the wings back over the abdomen as characterizes the Neoptera. The Diaphanopterodea are palaeopteran insects, had independently and evolved a different wing-folding mechanism. Ephemeroptera and Odonata are Paleoptera, which cannot fold their wings, whereas the Plecoptera are Neoptera, which can fold their wings over their back, so they are not closely related.

Neoptera is a major group of insects that includes almost all the winged insects and specifically those measured through the ability to fold their wings back over their abdomen. Neopterous insects include beetles, flies, wasps, butterflies. The Exopterygota are hemimetabolous neopterans show incomplete metamorphosis in which the wing buds are externally able to be seen before the adult stage and when no pupa or chrysalis stage occurs . The Endopterygota are holometabolous insects show complete metamorphosis, with distinctive larval, pupal, and adult stages in which the wings develop inside the body during the larval stage and only become external appendages during the pupa or chrysalis stage. Neoptera of species go through complete metamorphosis.

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