Effects of okra varieties and aphid suppression methods on the cotton aphid Aphis gossypii and associated natural enemies, and yield.

Two field experiments were carried out in Yaounde, Cameroon to investigate the effects of okra variety on the cotton aphid Aphis gossypii Glover and its natural enemies, and the yield. In year 1 experiment, a fully crossed factors of okra variety (Cafeier, Clemson spineless) and aphid suppression method (imidacloprid and control) was implemented on a randomised complete block design, with four replicates of each treatment (four in total). In year 2 experiment, we tested three methods of aphid suppression (imidacloprid, neem and control) on three okra varieties (Cafeier, Clemson spineless and Hire) in a randomised complete block design of four replicates. Blocks comprised beds that were subdivided each into three rows (year 1 experiment) or five rows (year 2 experiment). Population monitoring of aphids and natural enemies started four weeks after okra planting and repeated every two weeks until harvest. The number of aphids, associated predators (spiders, larvae of coccinellids, syrphids and lacewings), and parasitised aphids were recorded on three leaves selected each in the low, middle and apex of plants in the middle row of each bed. In parallel, we recorded the developmental stage of the plant and the number of leaves. Mature fruits were harvested daily (for Clemson variety) or every other day (for Cafeier and Hire variety) on the middle row of each bed. We summarised data as densities of aphids and specific predators, and aphid parasitisation rate per plant and submit the variables to generalised linear models to analyse effects of okra variety and aphid suppression method. Yield parameters included the number of fruits and fresh weight per plant and were analysed with a two-way ANOVA to assess the interaction between okra variety and aphid suppression.