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

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 sampli ng took place during four periods of the year: March, May, October and Nove mber. Amongst the insects captured were some economically important rice pe sts (Nilaparvata lugens, Sogatella furcifera, Nephotettix sop. and Cnaphalo crocis medinalis), some of their natural enemies, and also pest aphids (e.g . Lipaphis erysimi, Aphis gossypii and Rhopalosiphum rufiabdominalis). We f ound that insect aerial densities aloft often remained high until late in t he night, and we deduced from this that migration over distances of tens, o r even hundreds of kilometres was in progress-movements which would lead to redistribution of both pest and beneficial insects over large areas of nor theast India. Differences between aerial densities and migration rates foun d for the 4 months are interpreted in terms of seasonal cropping patterns a nd weather, and aerial densities of N. lugens, C. medinalis, aphids, and th e mirid Cyrtorhinus lividipennis are compared with values found from aerial netting studies in other geographical regions.