Incidence of the vectors of tristeza virus in Darjeeling hills

Six aphid vectors of tristeza virus, viz, Toxoptera citricidus Kirkaldy, T. aurantii Boyerdx Fonscolombe, Sinomeougoura citricolla Vander Gat, Aphis gossypii Glover, A. spiraecola Patch and A. craccivora Koch were found to occur in orange orchards of Darjeeling hills. Among these, the former four species were more widespread. High population of all these insects was found during postmonsoon months (August-September) when the average maximum and minimum temperatures ranged between 19.8° and 24.3°C, and 14.6° and 19.3°C, respectively. The extent of aerial trapping of them in yellow pan traps was maximum during 0ctober:November and they appeared to be most active at 10–11 IST. They showed diierential preference for different citrus and non-citrus hosts, and normally overwinter in ornamentals, field crops, weeds, wild trees and shrubs depending upon the species of aphids.