Impact of density of Aphis craccivora (Aphididae) on growth and yield of susceptible and resistant cowpea cultivars

Abstract

SummaryImpact of initial density of cowpea aphid Aphis craccivora Koch (Aphididae) at infestation on the growth and yield of aphid‐susceptible cowpea cultivar ICV‐1 and aphid‐resistant cultivar ICV‐12, was investigated. 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 after infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per plant and number of seeds per pod) were recorded. Due to the occurrence of parthenogenesis and changes in population dynamics during infestations, aphid densities were converted into cumulative cowpea aphid‐days, to facilitate data analyses and interpretation. ANOVA indicated that there was significant (P=s 0.05) difference in aphid‐day accumulations between the two cultivars when infested at the seedling stage. Accumulations on cv. ICV‐1 were greater than on cv. ICV‐12. However, no such differences between the cultivars were detected when plants were infested at flowering and podding stages. Therefore, the seedling stage was used for comparisons of the impact of cowpea aphid‐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 growth deformities which were not observed on ICV‐12 plants. Regression analyses revealed substantial reductions in the growth and yield parameters of ICV‐1 relative to ICV‐12. Overall, cowpea aphid‐days provided a convenient and reliable method for studying the aphid population dynamics and the subsequent impact on plant growth and yield performance.