INSECTS 



A KNOWLEDGE of the life-histoiy of an insect or 

 fungus is essential whenever it is a question of de- 

 stroying it, for there is often only one period in its 

 life when it is vulnerable, or when we can get at it 

 so as to attack it with success. Generally speaking, 

 there are four distinct stages in the lives of all insects : 

 (i) the egg, (2) the larva, maggot, grub or caterpillar, 

 (3) the chrysalis, nymph or pupa, and (4) the perfect 

 insect or imago. The true pupal stage is absent in 

 the case of mites and spiders, whilst in that of some 

 insects, such as aphides and leaf-hoppers, there is no 

 pupal stage similar to that existing in the case of a 

 moth, where the pupa is quiescent, and does not feed. 



Those insects which have a quiescent pupal stage, 

 for the conversion of the caterpillar, maggot or grub 

 into the adult form, are said to undergo a " complete 

 metamorphosis," and beetles, sawflies and flies undergo 

 such a change, as well as moths. Aphides, scale- 

 insects, leaf-hoppers and bugs undergo what is 

 called an "incomplete metamorphosis," wherein the 

 changes between the larva and adult are gradual, 

 the insect in the pupal stage resembling that in the 

 larval stage, except that '' wing-buds " appear, these 

 giving place at the next moult to fully developed 

 wings, and the insect then becoming perfect. During 



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