FOOD 241 



factors influencing the nutrition of the host-plants are reflected 

 in corresponding deviations in the reproductive capacity of the 

 aphid as shown below. 



Table XI. 



Treatment of Plants. 

 (Longpod Broad Beans.) 



Reproduction of Aphides. 



Grown in sand, treated with tap water 

 only 



The same, but watered with complete 

 nutritive solution .... 



Grown in standard soil 



The same treated with complete artificial 

 fertilisers ..... 



Control : taken as 100 



225 

 140 



200 



These figures represent, as before, the mean number of aphides 

 produced (on five plants in each experiment) by a single apterous 

 viviparous female per plant over a fourteen-day period. 



The familiar practice of pinching off the growing points, along 

 with the adjacent young leaves of bean plants, has also a very 

 marked influence on the number of progeny produced by Aphis 

 rumicis in a given time. In one series of five plants, in which this 

 treatment had been carried out, the mean reproductive rate of 

 the aphid was 104-8 (in fourteen days), while for plants that 

 remained intact the mean reproductive rate was more than three 

 times as high, viz., 335-2. It appears, from this experiment, that 

 the cell-sap of the young growing tissue of the host-plant is of a 

 very definitely higher nutritive value as food for the aphid than 

 the older tissues. Screening experiments, cutting off varying 

 amounts of daylight and thereby reducing the photosynthetic 

 activity of the host-plants, suppprt the conclusion that the 

 nutrition of the latter affects the metabolism of the insect, since 

 aphides on the most heavily screened plants produced the lowest 

 number of progeny in a given time. 



In further illustration of the influence of food upon insect 

 metabolism as expressed by fecundity, and also by the duration 

 of life, experiments by Simmons and Ellington (1925) with regard 



