WHAT ARE IMMATURE INSECTS 



DEVELOPMENT OF INSECTS. — When an egg and a sperm unite 

 to form one cell fertilization results and the embryo begins to develop 

 within the eggshell. This is called embryonic development and all 

 that takes place after hatching or birth is postembryonic development. 

 The life cycle is completed when the insect is fully grown and capable 

 of producing young. 



METAMORPHOSIS. — The term metamorphosis is derived from 

 the Greek words, nieta, change, and morphe, form, designating a 

 change of form. The plural is metamorphoses. It is defined as the ser- 

 ies of changes through which an insect passes in its growth from the 

 egg through the larva and pupa to the adult, or from the egg through 

 the nymph to the adult. 



a) Gradual or simple metamorphosis. — In many insect species the 



young are very much similar to 

 the adult externally, except for the 

 complete absence of wings. But 

 after a period of growth the wing 

 may appear, attached to the out- 

 side of the body as small wing 

 pads. The more developed the 

 young insect becomes, the more 

 it resembles its parents. Such a 

 development is called a gradual 

 or simple metamorphosis. The 

 young of such insects are called 

 nymphs. They commonly have 

 the same habits as their parents 

 and the nymphs and adults fre- 

 quently feed together. An example is the aphids where both adult and 

 young are habitually found associated on the same plant. Grasshop- 

 per nymphs and adults both eat grasses and clovers and may be found 

 hopping about together in the pastures. The insects of gradual or 

 simple metamorphosis include the orders Plecoptera, Ephemeroptera, 

 Odonata, Embioptera, Orthoptera, Isoptera, Dermaptera, Thysanoptera, 

 Corrodentia, Mallophaga, Anoplura, Hemiptera and Homoptera. All 

 these insects are collectively known as the Heterometabola. 



b) Complete or complex metamorphosis. — In this type of meta- 

 morphosis, the young are very different from their adults. There 

 are no external traces of wings. The young are known as larvae 

 and the adult is preceded by a pupal stage. The insects having 

 this type of metamorphosis are collectively called the Hoio- 

 metaJboia and include the orders Coleoptera, Neuroptera, Tri- 

 choptera, Lepidoptera, Mecoptera, Diptera, Siphonaptera, Strep- 

 siptera and Hymenoptera. 



Fig. 1. The life stages of chinch bug, 

 Blissus leucopterus (Say) : a-e, 1st 

 to 5th instar nymphs; f, adult; g, 

 eggs. (U.S.D.A.) 



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