32 ASSOCIATION OF ECONOMIC ENTOMOLOGISTS. 



period of 106 days. On the 1st of May aphides of the first two 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: on the 1st of August. 7 genera- 

 rions. 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. 

 Lasius nkjer americanus^ from April S 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 30th of October. A few oviparous 

 females were still living indoors Xovember 28. Males and females 

 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 daytime temperature of the insectary usually ranging 

 from 60° to 66° F. "We have had two instances of females whose 

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

 ductive aberration was exhibited by a viviparous female taken m the 

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

 insectary, where within the next few days she gave birth to G voting 

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

 tions for a few days, molted and acquired wing-, and afterwards 

 produced 21 more young. 



The number of molts is invariably four, and reproduction follows 

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

 next day. In 36 instances, of which exact record was kept, the 

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

 an average of 11. Any one disposed to calculate the theoretical 

 reproductive capacity of this specie- can easily do so from the data 

 given — 1:2 mean generation- and a multiplication ratio of 11. 



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

 because 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. 



