Resistance in lima bean to Aphis craccivora (Hemiptera: Aphididae)

The cowpea aphid (Aphis craccivora) can be an important pest on lima bean (Phaseolus lunatus L.). The objective of this work was to evaluate the effect of different genotypes of lima bean on the biology of A. craccivora and to identify possible sources of resistance to aphids under laboratory conditions. Two trials were set up, an antibiosis and a free-choice antixenosis test. Furthermore, the density of the trichomes on the leaf surface was determined for each genotype. Aphid life table parameters were similar in the antibiosis experiments for all of the genotypes tested. The calculated life table for the lima bean genotype used several parameters, namely Net Reproduction Rate (R-o)=49.23; Time interval between each generation (T)=10.24, Intrinsic rate of natural increase (r(m))=0.38; Finite rate of population increase ()=1.46 and Time for population to duplicate (TD)=1.82. The results of non-preference tests showed that genotype UFPI-887 exhibited antixenosis resistance when compared to genotypes UFPI-882 and UFPI-881. The trichome density average varied from 126.29 trichomes/mm(2) in genotype UFPI-882 to 42.20 trichomes/mm(2) in genotype UFPI-883. There was no correlation between trichome density in the leaves and no preference of A. craccivora for leaves of P. lunatus.