62 Biological Studies of A|)his rumicis 



The wide range of variation in the numbers on each variety, 

 is probably largely due to the variable fertihty of the agamic 

 females. 



In August and September 1913, 30 a. v. ??, offspring of wild w. v. ?? 

 of Aphifi rumicis, were isolated on broad bean in a greenhouse, with a 

 temperature varying from 62° F. to 85° F. The daily reproduction and 

 total offspring produced by each mother were recorded. The maximum 

 number of young born in any one day was 8. The minimum being 1. 

 The maximum total number produced was 45 and the minimum 0. 

 Three examples are given showing a low figure, a medium figure and a 

 maximum figure of reproduction. 



Temp.° F. m fi7 77 70 77 77 85 80 70 77 65 70 65 ^Sy^^ aphids 



August, 1913 19 20 21 22 23 24 25 26 27 28 29 30 31 production produced" 



Plant 1 003121032000— 1-7 12 



, 2 6 2 2 6 1 1 2 — 20 20 



„3 552525344460— 4-1 45 



It should be noted, however, that these aphids were taken towards 

 the end of the season, and the history of the previous generation was 

 not known. 



There would appear to be some relation between the time of the 

 year and the degree of infestation of plants. 



Recorded observations of marked decrease in the reproduction of 

 aphids during high summer temperatures, indicate an association of 

 temperature and the season of the year with the "dryness" of food 

 plants as contrasted \ath. the young succulent growth of spring and 

 early summer. It seems feasible to expect as a result of these factors, 

 a seasonal adaptation of aphids to the varying seasonal conditions. The 

 number of the viviparous generation used in experiments may therefore 

 be an important consideration when results obtained at different periods 

 of the season are compared. 



In my experiments, there was a marked decrease in the numbers of 

 aphids produced towards September and October, probably to some 

 extent due to lower temperature conditions and to the appearance of 

 sexual forms in the cultures ; but cultures, carried on throughout winter 

 in a warm greenhouse, also produced few aphids in comparison with 

 the reproduction in June. To some extent the appearance of sexual 

 forms in each generation accounts for this, but my observations indicate 

 that the greatest reproduction occurs with the early viviparous genera- 

 tions. 



