BIOLOGICAL STUDIES OF APHIS RUMICIS LINN. FACTORS AFFECTING THE INFESTATION OF VICIA FABA WITH APHIS RUMICIS

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Abstract
SUMMARY: A technique has been developed, whereby the influence of various factors such as temperature, manurial treatment, soil conditions, age and variety of the plant on the infestation of beans by Aphis rumicis can be tested. Factors which influence the physiological activity of the plant, thereby affecting growth and the nature of the cell sap, affect also, through the food factor, the progress of the aphis infestation. Experiments have been carried out during four years, the methods employed being fully described. The chief features of the technique are: (a) The same strain of aphis was used throughout and infestations were made with sisters of the same generation for all comparable series. (b) The same variety of beans was used throughout and with comparable series the plants were always of the same age. (c) The reproduction period in all comparable series extended approximately over the same days, so that temperature and other climatic factors were the same for all the series. The experiments were in series, each series consisting of five plants, each plant being infected with one a.v. female. The aphids present on each plant at the end of a definite reproduction period were counted and the mean of the counts for the five plants was taken as the mean infestation figure for the series concerned. Temperature influences the developmental period of the aphids and also the daily production of young, thereby affecting the infestation figures, so that the reproduction period for all comparable series was taken during the same days. Significant differences in infestation have been obtained with certain series, these differences being considered as indicating differences in the feeding value of the plants in the different series. Beana grown in soil treated with complete mineral manures became slightly more heavily infested than those grown in unmanured soil. In unmanured sand low infestation figures were obtained. Beans grown in sand watered with normal culture solution gave higher infestation figures than those grown in soil watered with the same solution. Beans supplied with increased potash indicated increased infestation figures, whereas with low potash a decrease was obtained. Beans grown in sand watered with culture solution containing increased MgSO4 showed a marked increase in infestation. Experiments repeated for three years, in which varying amounts of daylight were available for the plants, show that with reduction of the light, a decrease in infestation is obtained. Similarly in Winter when artificial light, in excess of the ordinary daylight, was used, an increase in infestation was obtained compared with those plants which only received daylight. This is probably associated with the carbohydrate content of the plant sap and the decrease in young growth. Bean plants six weeks older than the controls gave a marked decrease in infestation figures. Beans grown in acid soil and in badly aerated soil conditions, did not show any difference in infestation, compared with the control series, but owing to the low temperature during the reproduction period the results are inconclusive. The relation between the optimum temperature for the growth of the host plant and that for the development and reproduction of the aphids is an important consideration with reference to outbreaks of aphis infestation. The results obtained in these experiments show that aphids react to physiological changes in the host plant. They problems have a wide application to plant‐sucking insects in general, but the experiments only represent a preliminary investigation of a wide and important subject.