No. 34-] HEMIPTERA OF CONNECTICUT: APHIDIDAE. 25 1 



overwintering eg-g a wingless female hatches in the spring and is 

 known as the stem mother. The stem mother does not deposit 

 eggs but produces living young, and is the first of a series of forms 

 reproducing in the same way and designated on this account vivi- 

 parous females. The young progeny of the stem mother begin at 

 once to feed upon the sap of the plant and in about two weeks, 

 more or less, according to the species and weather conditions, are 

 in turn ready to produce offspring. 



The first few spring generations may be wingless or at any time 

 winged individuals or an entire winged generation may appear 

 and fly away to fresh plants and there start new colonies where a 

 succession of generations are produced as before. Such a flight 

 is called the spring migration and with many species the migrants 

 desert the host plant upon which they have been feeding and seek 

 a plant of an entirely different species. Thus the aphid destruc- 

 tive to hops passes part of its life cycle upon plum trees. This 

 alternation of hosts is a point in the life history of aphids of great 

 economic significance, for it sometimes happens that a species can 

 be controlled on one plant and thus its attack upon the other or 

 alternate host be prevented. 



After a species has spent all or a part of the summer upon the 

 second host plant, winged individuals called fall migrants appear 

 and return to the same kind of plant, the winter host, upon which 

 the stem mother and spring generations had lived, and there con- 

 tinue to breed. Up to this time no males have appeared and all 

 of the forms, whether winged or wingless, have been females 

 giving birth to living young agamically as was the case with the 

 stem mother. 



But immediately following or soon after the fall migration there 

 are developed the true sexes — males and egg-laying females. 

 These oviparous females deposit one or few comparatively large 

 eggs in which stage the insect winters and from which the stem 

 mother hatches in the spring. 



It is to such an outline as the foregoing that a species whose life 

 history is unknown must be referred as a working basis. Any 

 variation of the general life cycle of the aphids, however, is not 

 a fair cause for surprise, for these insects have peculiar ways of 

 their own which sometimes seem very erratic. For instance, 

 besides the winter Q^fi;g on the winter host some species, as the 

 "alder blight" (Prociphihts tessellata) and the "woolly aphid of 

 the apple" (Eriosoma lanigerimi) , have a second method of passing 

 the cold season and that is as hibernating nymphs which remain in 

 hiding at the roots or in rubbish about the base of the summer host. 

 These hibernating nymphs come forth in the spring to feed, thus 

 giving continued generations upon a single food plant as well as a 

 cycle which includes a migration to an alternate host. 



The characters used for descriptions and keys are many but they 



