1921] Uichanco — Reproduction in the AphididcB 105 



means belittled. As has been stated above, adverse temperature 

 conditions evidently play a very important part in the determina- 

 tion of amphigony, and a uniformly mild temperature is appar- 

 ently conducive to an indefinite maintainance of parthenogenetic 

 reproduction. The point suggested, however, is that the effect of 

 continuous subjection of an aphid strain which normally undergoes 

 heterogony to mild temperature does not immediately become mani- 

 fest. But this fact does not preclude the possibility that the cumu- 

 lative effects on more than one yearly cycle of generations might 

 bring about a change in the method of reproduction to one of con- 

 tinuous parthenogenesis. I have no data bearing on the reaction 

 of the greenhouse aphids which reproduce continuously by partheno- 

 genesis to the adverse weather conditions outdoors during the fall 

 and winter months. 



I am not prepared to discuss from personal observations the rela- 

 tion between scarcity of food and the determination of amphigony. 

 There is apparently nothing in the literature wliich touches this 

 subject, except the statement of Tannreuther (1907) that "abun- 

 dance or scarcity of food is not a factor in determining the sex 

 in the case of the aphids," for which, however, he presents no 

 concrete experimental evidence. Of some possible interest in con- 

 nection with this problem are the experiments by G-regory (1917), 

 who found that by subjecting parthenogenetic individuals of Macro- 

 siphum pisi Kaltenbach (=lf. destructor Johnson) to varying 

 periods of starvation, in certain cases carrying her experiments to 

 the maximum possible points without killing the insects, she could 

 induce the production from apterous mothers of alate offspring, 

 which, as shown by her check cultures, would otherwise have been 

 apterous. It is, however, apparent from her paper, although she 

 does not state it, that the subsequent offspring of these starved 

 aphids were invariably parthenogenetic and that the production of 

 amphigonous individuals was not artificially induced by the treat- 

 ment. It is to be regretted that she did not carry her experiments 

 tlirough the succeeding generations after the mother; and the 

 question now arises as to whether the production of amphigonous 

 individuals is induced only by the successive and cumulative effects 

 of starvation on several generations of parthenogenetic individuals. 

 One point is suggested by these experiments, and that is that, as 



