3i8 



Journal of Agricultural Research voi. xviii, no. 6 



acceleration in growth caused by later, higher temperatures, or vice 

 versa. Nevertheless the effect of the temperature was so marked that 

 it was felt to be worth while to call attention to it in this manner. 



In this connection it might be well to note the fact that the season of 

 1 91 5, at Vienna, Va., was an excellent one for the rearing of aphids, since 

 the summer was cool throughout and the humidity was high. Results 

 obtained during other years seem to indicate that excessively high tem- 

 peratures, at least when accompanied by dry weather, may have a direct 

 effect, rather than an inverse one, upon the length of this period. It may 

 be, however, that such effects are due to excessive drought rather than 

 to high temperatures. 



REPRODUCTION 



The average number of young produced by 102 insects was 28.1 each. 

 The insects used in obtaining these figures were secured from all the 



// 

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<3 

 P' 



GO 

 P'O 



Fig. I. — Effect of temperature upon the duration of the larval stages of the apple-grain aphis. 



summer generations. No difference was observed in this matter between 

 mothers occurring in the early summer, the middle of summer, and the 

 early fall. The average reproductive period for this insect was 17.9 

 days, giving an average of a little over 1.5 young per day for the entire 

 102 insects. 



This daily production varied somewhat with the season. The mothers 

 producing young during late September and October produced an 

 average of one or even less per day. Their reproductive period was 

 considerably longer, however, so that the total number of young 

 produced by one mother was 54, and the smallest was 12. The greatest 

 daily average was 3 young, the mother producing 54 young in 18 days. 

 This insect and one produced by the same mother also hold the record 

 for greatest single daily production, the two together producing 41 young 

 in 2 days. 



