Impact of predatory ants on two lepidopteran insect pests in Indian cauliflower agroecosystems

Abstract

The impact of predatory, agroecosystem-nesting ant species on the larval stages of the two major lepidopteran pests, the diamondback moth (DBM), Plutella xylostella and the black cutworm (BC), Agrotis ipsilon, in cauliflower agroecosystem in Uttar Pradesh, India, was investigated in farmers' fields. Field observations revealed that six ant species, the most important being Pheidole sp., preyed on the crop-damaging stages of DBM and BC. Bait experiments with larvae of DBM and BC, placed randomly on the ground, demonstrated significant active retrieval by Pheidole sp. Investigations on larval density of both the insect pests on cauliflower crops, located within 1-5 m distances from nests of Pheidole sp., revealed a significant increase in the level of infestation of the crop plants with increasing distance from the ant nests. While a significant negative correlation was found between infested plants with low larval densities, a positive correlation was found between plants with high larval densities with regard to the distance of crop plant location from the ant nest. Ant-inclusion and -exclusion experiments under field conditions further confirmed the role of predatory ants, with Pheidole sp. having the major impact in the direct retrieval of the lepidopteran larvae from the crop plants. A significant difference was found in the leaf area damaged by BC larvae between the ant-included and -excluded potted plants during the 6-h observation period. Thus, this study provides direct evidence of the role of ants in actively searching and directly preying on the larval stages of DBM and BC, on cauliflower plants. Moreover, we demonstrate that in ephemeral, annual cropping agroecosystems, predatory ants are important natural enemies of lepidopteran pests, playing a significant role in plant protection. © 2007 The Authors.