RESISTANCE TO APHIS CRACCIVORA (HOMOPTERA:APHIDIDAE) IN SELECTED VARIETIES OF COWPEA

Nearly 200 varieties of cowpea, Vigna unguiculata (L.) Walp, were screened for resistance to the cowpea aphid, Aphis craccivora Koch. Three varieties known to be resistant in West Africa were highly susceptible to an aphid population from the southern United States. Four other varieties, however, inhibited growth of the southern United States population both in the laboratory and in the field. Life-table comparisons using a resistant and a susceptible variety revealed a three-fold difference in the intrinsic rate of increase and a more than twenty-fold difference in the net reproductive rate. High nymphal mortality and low fecundity on resistant plants were largely responsible for these differences.