INFLUENCE OF WEEDS ON DISPERSION OF INSECT PESTS AND PREDATORS IN BRINJAL AND GROUNDNUT CROP ECOSYSTEM

A heterogenous agricultural habitat with brinjal, groundnut and a host of associated weeds was selected to study the influence of weeds on dispersion of insect pests and predators in Tiruvallur district of Tamil Nadu, India.In the field experiment, impact of weed on diversity on pests and predators in two weed management practices was quantified in weedy and control plots.Fourteen insect species were found to infest brinjal crop and seven species on groundnut crop and associated weed species.Population of Henosepilachna vigintocto punctata and Caliothrips indicus were observed throughout the year.Allowing weeds to grow in weedy plots, increased the population of predators and reduced pests in brinjal and groundnut crops.On both the crops, pests population declined as weed diversity increased.The weeds Solanum xanthocarpum, Solanum nigrum and Physali sminima served as alternate hosts for H. vigintocto punctata during the absence of main crop of brinjal.Population of C. indicus dispersed from Achyranthes aspera and Justicia simplex to brinjal during the early stage of the crop.Upon senescence of brinjal crop they dispersed to groundnut and Tridax procumbens.Echinocloa colona and Euphorbia hirta were the important reservoirs for Aphis gossypii during the harvesting stage of groundnut.Hibiscus sabdariffa gave regular support for Bemisia tabacci and Amrasca devastans.The dispersal of pest and the predator complex is discussed in relation to the abiotic factors of the environment and the relative density of the weeds.Hence, in addition to varying competitiveness, the pest management practices may depend on how the insects are influenced by adjacent plant and weed diversity.The results indicated that brinjal and groundnut crops might benefit from stronger natural pest control with minimum weed management practices.