Demographic parameters of cowpea aphid Aphis craccivora (Homoptera: Aphididae) on different Botswana cowpea landraces

The variation in demographic parameters (namely survival and fecundity, intrinsic rate of natural increase pre-reproductive period and relative growth rate) was used to assess the resistance of cowpea landraces (namely B261-B, B383, B013-F, B339 and Blackeye, as a check) against cowpea aphid (Aphis craccivora Koch). The experiment was carried out from 18 March 2011 to 5 April 2011. The demographic parameters of A. craccivora differed significantly among varieties, supporting our prediction that cowpea landraces resistant to cowpea aphid would have a significant effect on the demographic parameters of the aphid. We recorded significantly lower survival, fecundity, intrinsic natural rate of increase and relative growth rate on the landraces B261-B and B383 compared with the other landraces. A significant delay in the pre-reproductive period was also found on B261-B and B383. The results showed that landraces B261-B and B383 have an increased level of resistance as shown by the extended pre-reproductive period and the reduction in population growth rate, survival and fecundity. This information will be used in the characterization of the landraces before being incorporated in the breeding programme in Botswana.