Studies on abundance, impact and natural enemies of insect pests of Okra and Chilies and efficacy of neem products in their control

Abstract

Studies on abundance, impact and natural enemies of insect pests of okra and chilies and efficacy of neem products in their control were conducted at Kibwezi (2°21-5'S, 38°2-5'E) a semi arid region of the Eastern province of Kenya. Okra seeds were planted directly, while one-month old chili seedlings were transplanted in 4 x 3m. Plots in the field during the months of September 1998 and January 1999 in two cropping seasons. The plots were left for natural infestations but various species of insect pests were noted. Sampling was carried out and insect pests that infested okra and chilies at certain stages of the crops' growth were identified. Aphids and whiteflies were found to transmit leaf curl disease to the chilies whereas, flower beetles, flower thrips and fruit borers, which, infested the fruits from reproductive stage to maturity, damage the fruits of both crops. In some instances and at certain growth stages, insect pest population, percentage damaged leaves and associated yields loss differed significantly between the pesticides treated and unprotected (control) plots. Foliar damage on okra resulted from the feeding habits of caterpillars, leaf beetles while that of chilies resulted from the leaf curl virus disease infection. A 19.3% and 23.5% yield loss for okra and growth stages resulted in gains of the avoidable yield loss from insect pest infestation. The most common natural enemies of aphids comprised of various species of coccinellid beetles, parasitic wasps and the predotory larvae of syrphid flies. A carabid beetle and both larval and adult forms of coccinellid beetles preyed on red spider mites. They significantly reduced the insect pest population mostly on okra and chilies. A formulation of 20ml/1 of neem oil was more effective against most pest opulations on okra and chilies than the 15ml/1-neem oil, 25 and 50g/1-neem seed kernel extract (NSKE) obtained by grinding the seed]. However, the neem products conserved populations of natural enemies and other beneficial insects. All the neem formulations were effective in reducing the amount of foliar damage on okra. Although similar formulations of neem products had varied effects on the yield loss from insect infestations on both the crops, the marketable yield was improved by all the formulations. Results from these studies can be enhanced by conducting other research to establish the distribution and infestation of insect pests, their ysiological impact and dose optimization of neem products and associated yield loss within and between localities on both the crops.