ECONOMIC ENTOMOLGY. 223 



deformed and ruined. When three days old, the larva changes 

 its skin ; this is repeated three times at similar intervals. For the 

 greater number, these metamorphoses produce but little change in 

 appearance beyond a small tail, which develops at the end of the 

 abdomen. When about nine days old, the female aphis (condi- 

 tions of food and temperature being favourable) begin propagating 

 their species by giving birth to living larvae without having had 

 any connection with the male. This has been described by 

 Professor Owen as follows : — 



" This larva, if circumstances of food and warmth be favour- 

 able, will produce a brood — indeed, a succession of broods of larvse 

 — like itself without connection with the male. In fact, no winged 

 males will have appeared, [f the virgin progeny be also kept 

 from any access to the male, each will again produce a brood of 

 the same number of aphides, and carefully prosecuted experi- 

 ments have shown that this procreation from a virgin mother will 

 continue to the eleventh generation before the spermatic virtue of 

 the ancestral coitus has been exhausted." 



In favourable seasons, a certain portion of the third and 

 fourth of these viviparous generations undergo special changes. 

 At the first moulting small processes are observed on the back 

 These at successive moultings become largely developed, and 

 after the fourth and last change of skin appear as large, fully- 

 formed, transparent wings, on which the insect can fly away to 

 fresh fields and pastures new. These winged aphides produced 

 during the summer are always females. When two or three days 

 old they take their flight to found new colonies. After the fourth 

 generation, no further winged females are produced. 



Towards the end of autumn the generations, usually eleven in 

 number, approach their close, and the last brood produces a 

 certain number of winged males, who fly off in search of partners. 

 Reproduction then follows its normal course. The females, after 

 marriage, give birth to no more living larvae and produce only 

 eggs. These remain during the winter protected by impervious 

 shells from the cold, which would destroy the soft larvae. In the 

 spring these are hatched, producing larvae as already described, 

 who in their turn repeat the viviparous generations. 



This is a brief outline of the life-history of the aphis family, 



