4 FARMEES BULLETIN 804. . 



APHIDS IN GENERAL. 



Aphids, or insects of the family Aphididae, have a development 

 Avhich is remarkable in several ways. Eggs laid in the autumn hatch 

 in the spring about the time when vegetation revives. From these 

 Avinter eggs is produced a generation of females, usually wingless, 

 which reproduce without the intervention of males {agamic repro- 

 duction), man}^ species giving birth to living young. The adult 

 aphids of the first generation are termed stem-mothers. The off- 

 spring of the stem-mothers (second generation) may be winged or 

 Avingless, or both forms may occur. They reproduce without the 

 intervention of males, some species being oviparous, or egg laying, 

 and depositing eggs which do not require fertilization for develop- 

 ment, while others are viviparous — that is, they bring forth young 

 alive, the eggs developing and hatching within the body of the 

 parent. 



A succession of generations may be produced in this way until the 

 approach of autumn, when the true sexes appear and the females 

 deposits eggs; or a species perhaps may be more or less biennial, some 

 individuals producing true sexes only every second year. In still 

 other species, the true sexes of which are at present unknown, repro- 

 duction without the intervention of males continues for a series of 

 years. 



The same species of aphid usually exhibits several forms, as wing- 

 less agamic females, winged agamic females, and the true sexual 

 forms. In the last the male may be winged and the female wingless, 

 or both sexes may be wingless. The different generations of a given 

 species may vary more or less in appearance, and in some instances 

 this is the case to such an extent that they appear to belong to dis- 

 tinct species. 



Aphids feed upon sap which is sucked up through a beak pushed 

 down into the tissues of the plant. Their presence on plants fre- 

 quently is indicated by a curled and distorted condition of foliage, 

 though this is not always so. When the insects are abundant the 

 drain upon the plant is very great, interfering with its proper growth 

 and development, and in extreme cases causing the death of infested 

 parts. The leaves and shoots of plants infested by aphids are fre- 

 quently seen to be covered with a black substance, as if dusted with 

 soot. This is due to a black fungus which grows on the " honeydew " 

 excreted by the aphids and is not especially injurious, though often 

 objectionable as marring the appearance of the plants and fruit. 

 Honeydew may be produced in such quantities as to coat the leaves 

 and is attractive to various species of ants and wasps, which are 

 often seen attending the aphids or frequenting plants infested by 

 them. The ants of themselves are not usually the cause of trouble 

 but merely denote the presence of the aphids. 



