32 ASSOCIATION OF ECONOMIC ENTOMOLOGISTS, 



period of lOG days. On the 1st of May aphides of the -first tivo gen- 

 erations may coexist in the field ; on the 1st of June, those of the 

 first three generations; on the 1st of July, 5 generations, from the 

 second to the sixth, inclusive; (m the 1st of August, 7 genera- 

 tions, from the fourth to the tenth inclusive; on the 1st of Septem- 

 ber, 9 generations, from the seventh to the fifteenth; and on the 1st 

 of October, 10 generations, from the seventh to the sixteenth. 



We have found eggs hatching in the nests of the small brown ant, 

 Lasi'us niger mnericanus^ from April 8 to May 22, a period of 44 

 days. Our earliest record of the occurrence of the bisexual ovip- 

 arous generation in fall was September 5, and the latest births of 

 this generation occurred on the 80th of October. A few oviparous 

 females were still living indoors November 28. Males and feuiales 

 were first seen pairing September 30, and this is also the earliest 

 date at which eggs have been found. 



The oviparous generation does not correspond to any single one of 

 the annual series, but bisexual forms may appear in any generation 

 in existence at the time when conditions are right for their develop- 

 ment. In our insectary work of this year sexual forms originated 

 in September and October from representatives of 5 different gen- 

 erations, varying from the seventh to the eleventh of a series reared 

 in confinement after June 22. This appearance of the sexes is evi- 

 dently favored, if not actually produced, by a low temperature — 

 a fact illustrated by the occurrence of sexual forms, September 5, 

 1905, when the weather was extremely cool for that time of the 

 year, the daytiuie temj)erature of the insectary usually ranging 

 from 60° to ()()° F. We have had two instances of females whose 

 first young were viviparous and the last oviparous. Another repro- 

 ductive aberration was exhibited l)y a viviparous female taken in the 

 field in the pupa stage on the 23d of Jinie, and transferred to the 

 insectary, where within the next few days she ^ave birth to 6 young 

 previous to her final molt. She then suspended reproductive opera- 

 tions for a few days, molted and acquired Avings, and afterwards 

 "produ.ced 21 more young. 



The number of molts is invarial)ly four, aiul reproduction follows 

 sometmies within a few hours of the last molt, and usually by the 

 next day. In 3(') instances, of which exact record was kept, the 

 niunber of living young varied from 20 to 84 for each female, with 

 an average of 41. Any one disposed to calculate the theoretical 

 reproductive capacity of this species can easily do so from the data 

 given — 12 mean generations and a multiplication ratio of 41. 



Such a calculation is, of course, worthless for any scientific end, 

 becau-^e it involves a physical impossibility — that is, the maintenance 

 of optimum conditions for all the progeny of a single female the 

 whole season through. It is conceivable, however, if not believable, 



