IMPACT OF DENSITY OF APHIS-CRACCIVORA (APHIDIDAE) ON GROWTH AND YIELDOF SUSCEPTIBLE AND RESISTANT COWPEA CULTIVARS

Impact of initial density of cowpea aphid Aphis craccivora Koch (Aphid idae) at infestation on the growth and yield of aphid-susceptible cowp ea cultivar ICV-1 and aphid-resistant cultivar ICV-12, was investigate d. Plants at the seedling, flowering and podding stages of development were infested with five aphid densities consisting of 0, 2, 5, 10 and 20 aphids per plant and maintained for 22 days. Extended leaf heights of plants and aphid counts were recorded at 7, 12, 17 and 22 days aft er infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per pla nt and number of seeds per pod) were recorded. Due to the occurrence o f parthenogenesis and changes in population dynamics during infestatio ns, aphid densities were converted into cumulative cowpea aphid-days, to facilitate data analyses and interpretation. ANOVA indicated that t here was significant (P less than or equal to 0.05) difference in aphi d-day accumulations between the two cultivars when infested at the see dling stage. Accumulations on cv. ICV-1 were greater than on cv. ICV-1 2. However, no such differences between the cultivars were detected wh en plants were infested at flowering and podding stages. Therefore, th e seedling stage was used for comparisons of the impact of cowpea aphi d-days on the growth and yield parameters of the two cultivars. At the 95% confidence intervals, ICV-12 plants were consistently taller than ICV-1 plants. Infested ICV-1 seedlings showed stunting and other grow th deformities which were not observed on ICV-12 plants. Regression an alyses revealed substantial reductions in the growth and yield paramet ers of ICV-1 relative to ICV-12. Overall, cowpea aphid-days provided a convenient and reliable method for studying the aphid population dyna mics and the subsequent impact on plant growth and yield performance.