THE PHYSIOLOGICAL ASSOCIATION BETWEEN APHIS CRACCIVORA KOCH AND VIGNA SESQUIPEDALIS FRUW.

In a greenhouse experiment, adult apterae of Aphis craccivora were either confined to the second trifoliate leaf of 19‐day‐old plants of Vigna sesquipedalis or allowed to move freely after infestation. When the aphids were confined the dry wt of the plant after 14 days infestation was 62% of the controls; when they were free to move, it was 29·5% of controls. When the second trifoliate leaf was infested, the rate of photosynthesis per unit leaf area decreased to 3·6% of its initial rate on day 10, when it was moribund. Over 10 days, the total photosynthesis of the infested leaf was 56% of the control but this was reduced to 32% if the longer life of the control (more than 20 days) was taken into account. Photosynthesis was not stimulated at any time. Respiration of the infested second trifoliate was little influenced by infestation until it became prematurely moribund. Infestation of the young third trifoliate was accompanied by a slower expansion of the second trifoliate and by increased photosynthesis by that leaf during the first 6 days: the photosynthetic rate per unit area of the second trifoliate was 1·18 and 1·34 times that of the control on days 3 and 6 respectively, but declined to 0·85 on day 10. Infestation reduced the quantity of photosynthate available for movement from the second trifoliate to normal sinks from over 80% to less than 1% of the amount produced. When the third trifoliate was infested and the second was given 14 CO 2 , the aphids were able to divert over 20% of translocated assimilate from its normal destination. The inhibition of vegetative growth is discussed in relation to these physiological changes.