POPULATION-DYNAMICS AND CLONAL COMPARISONS OF COWPEA APHID (HOMOPTERA, APHIDIDAE) ON RESISTANT AND SUSCEPTIBLE COWPEA CULTIVARS

Survivorship, growth, and reproductive performance of cowpea aphid, ap his craccivora Koch, were studied on whole plants and excised plant ti ssues of aphid-resistant ('ICV-12') and aphid-susceptible ('ICV-1') cu ltivars of cowpea, Vigna unguiculata (L.) Walp. In a greenhouse study, clonal populations derived from individuals that were originally coll ected from 5 different locations were studied on plants of the 2 culti vars to assess possible development of aphid biotypes. In the laborato ry, performance of 1 clone was studied on excised leaves, flowers, and pods to assess tissue localization and effect of injury on ICV-12 res istance. Aphid life table parameters measured included survivorship, r eproductive period, intrinsic rate of increase, net rate of reproducti on, number of generations and generation time. Aphid reproductive perf ormance and life table parameters were significantly reduced on seedli ngs and excised tissues of ICV-12 plants compared with ICV-1. Survivor ship, intrinsic rate of increase and net rate of reproduction of popul ations were most adversely affected. Antibiosis appeared to contribute to aphid resistance in ICV-12. Effects of excised ICV-12 foliage were stronger than those of flowers or pods. Thus, the resistant factor in ICV-12 apparently was based in seedling foliage. However, there were no differences among excised tissues of ICV-1. Trends in the results i ndicated that there was no variability among the different populations in their demographic statistics on each cultivar. Thus, there did not seem to be biotype development or breakdown of ICV-12 resistance in a ny of the A. craccivora populations.