Effect of Host-plant on the Resistance of Acyrthosiphon pisum (Harris) to Insecticides

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Abstract
By means of a laboratory spraying technique, ten comparisons were made of the resistance to rotenone of samples of adult apterous viviparous parthenogenetic females of the Pea Aphid, Acyrthosiphon pisum (Harris), reared on broad bean and on clover, respectively. In nine of the tests, the Aphids from clover were more resistant than those from broad bean, the ratios ranging from 1·1 to 2·5. These differences were not all significant. In the remaining test the Aphids. from broan bean showed a very small increase in resistance over the Aphids from clover which was not significant.The Aphids from the clover were generally smaller than those from broad bean. Figures are given to show that while the total amount of poison retained by the larger individuals from broad bean was more than that retained by the smaller individuals from clover, the amount of poison retained per unit body weight was greater with the smaller individuals. It appears, therefore, that while the results obtained might be due, at least partially, to the greater total weight of poison retained by the larger individuals from broad bean, the difference in resistance between the insects from broad bean and clover, respectively, might be even greater if the poison were applied on the basis of equal weight of poison per unit of body weight. Since the difference in resistance between the Aphids from the two host-plants did not appear to depend primarily on difference in size, the assumption might be made that it is due to difference in nutrition. It was found that Aphids reared on clover had a significantly higher proportion of dry matter in their composition than those reared on broad bean, which may be taken as evidence that differences due to nutrition are being produced. These may lead to differences in resistance.