64 Blulofjical Studies of x\i)hifs rumicis 



With Afhis rumicis it was found that small agamic females from 

 dwarf French beans, when transferred to beans, produced young which 

 developed into normal size. 



(c) The Injiuence of Tentqieralure and Huniidiiy on (he 

 Development of the Species, 



It was observed throughout the experiments that low temperatures 

 retarded the development period and the production of young over a 

 given period. For this reason figures of reproduction for one period 

 cannot be safely compared with those for another period, unless due 

 regard is paid to temperature conditions. Further it appears probable 

 that the maximum reproduction occurring in early summer, with a 

 decreasing reproduction later in the season, may be an expression of 

 adaptation, and that even with favourable conditions of food and 

 temperature with later generations, later in the year, the high repro- 

 duction figures of earher generations are not obtained. It is interesting 

 to compare Tables V and VI in this respect. Recorded observations 

 show that there is a decrease in the number of aphids during high 

 summer temperatures and experiment demonstrates that abnormally 

 high temperatures restrict the development: it has been pointed out 

 above, that the association of high summer temperatures vnih the 

 "dryness" of the food plants at that period, involves the factor of food 

 conditions Avith a possibihty of a seasonal adaptation of aphids. 



Afhis rumicis could not be. reared in winter in the warm dry air of 

 the laboratory, most of the young dying before reaching maturity; 

 whereas in a similar temperature in the humid atmosphere of the green- 

 house they developed normally, 



Headlee(4), found with Toxopfera graminum Rondani, that with a 

 constant humidity of 75 per cent., the development period from birth 

 to maturity varied according to the temperature. Variations in atmo- 

 spheric humidity (between about 37 per cent, to 100 per cent.) did not 

 have any marked effect on the metabohsm of the aphids. Similarly 

 variations of 20 degrees or so about the optimum temperature did not 

 produce any marked eflect. 



Klodnitski(5) also showed the retarding effect of low temperatures 

 on other species of aphids. It would appear that there is an optimum 

 temperature for development which may vary for different species. 



