HOW TO KNOW THE IMMATURE INSECTS 



Fig. 4. Metamorphosis and life stages. 



IMMATURE INSECTS. — From the previous figure of the insect life 

 stages, insects are seen to have two or three stages before they become 

 adult or imago. The stages, egg, young (nymph or larva) and pupa 

 are the immature stages of insects. We must consiaer all the life stages 

 which precede the adult stage. 



INSTARS. — Every insect during its growth sheds its skin one or 

 more times. This process is known as a mouh or ecdysis. The cast 

 skin is termed the exuviae (this term does not exist in the singular). 

 The intervals between moults are known as stages or stadia (singular, 

 stadium), and the form assumed by an insect during a particular sta- 

 dium is termed an instar. When an insect issues from the egg it is 

 said to be in its iirst instar; at the end of this stadium the first moult 

 occurs and the insect then assumes its second instar, and so on. The 

 final instar is represented by the fully mature form and is known as 

 the aduh or imago. 



Ist moult 2nd moult 

 hatch 1st ^i nstar > 2nd instar > 3rd instar 



EGG ^MIHHMHIiM^ LARVA ^■■■■■H^HM^HM 



nth moult 3rd moult 



emerge pupate ♦-(n+l)th instar^^ 4th instar < 



ADULT ^H-H^i FUPA ^■»MMMMHiHHi^HiiiH^MiiHHa^Ha^^^»iMi 



NTMBER OF INSTARS = number of moults + 1 



Fig. 5. Life stages and instars. 



THE IMPORTANCE OF IMMATURE INSECTS 



NUMBER OF SPECIES OF INSECTS. — According to Z. P. Metcalf 

 (Ent. News 51: 219-222. 1940), approximately 1,500,000 species have 

 been described during the period from 1758 to 1940. This would make 

 the insects occupy almost eighty per cent of the species of the whole 

 animal kingdom. 



