Whitefly [Bemisia tabaci (Genn.)] on Cassava: Seasonal Variation and Varietal Preference

Abstract

A simple method was developed for the estimation of whitefly [Bemisia tabaci (Genn.)] population on cassava at Central Tuber Crops Research Institute, Thiruvananthapuram, India. The maximum number of late instars of whitefly was found on the 8  th and 9th leaf from the top. The late instars of whitefly could be counted on the 8  th leaf in situ without any aid. The nymphal count on the 8th leaf showed a significant correlation with the adult population of the previous month. The tender most leaf of the cassava plant took 20-22 days to become the 8  th leaf from top. The life cycle of whitefly was completed in about 17-30 days with an average of 25 days. The time taken for the growth of the tender most leaf to the 8  th leaf position and the development of the insect from egg to late instar synchronised. Each cassava leaf has on an average seven leaflets and there was a preference for middle leaflet (4  th) for egg laying. Development and population build up of  B. tabaci was seen affected by temperature and humidity and not by rainfall and sunshine. Significant seasonal variation and varietal preference were recorded in the population. The varietal preference changed according to season and the host preferred by adult and nymph also varied, which indicated that the preference of host for feeding and development were not the same.