Seasonal variation in the windborne movement of insect pests over northeast India

Abstract

This paper describes the use of a kytoon-supported net to sample the insect fauna flying at about 150 m above a site in West Bengal, India. The sampling took place during four periods of the year: March, May, October and November. Amongst the insects captured were some economically important rice pests (Nilaparvata lugens, Sogatella furcifera, Nephotettix spp. and Cnaphalocrocis medinalis), some of their natural enemies, and also pest aphids (e.g. Lipaphis erysimi, Aphis gossypii and Rhopalosiphum rufiabdominalis). We found thatinsectaerialdensities aloftoften remained high untillate in the night, and we deduced from this that migration over distances of tens, or even hundreds of kilometres was in progress-movements which would lead to redistribution of both pest and beneficial insects over large areas of northeast India. Differences between aerialdensities and migration rates found for the 4 months are interpreted in terms of seasonal cropping patterns and weather, and aerial densities of N. lugens, C. medinalis, aphids, and the mirid Cyrtorhinus lividipennis are compared with values found from aerial netting studies in other geographical regions.