Influence of meteorological factors on population build-up of pod weevil, Apion clavipes Gerst. on main season pigeonpea under conditions of North Bihar (India)

Studies on the influence of two important meteorological parameters, viz., average ambient temperature and relative humidity on the population build-up of the pod weevil (Apoin clavipes Gerst.) were made on main season pigeon pea cv. Bahar, during 1990–91 and 1991–92 crop seasons. The pest remained active from the second week of January to the last week of March, synchronising with the flowering-podding and full podding stages of the crop. Its mean larval population varied considerably during the two crop seasons from 0.17 and 7.13, and 0.47 and 13.42 larvae/plant in 1990–91 and 1991–92, respectively. However, the peak activity was observed during the last week of February to second week of March with the mean larval population varying between 7.23 and 7.37/plant on pooled basis, when the average maximum and minimum temperatures and relative humidity were between 27.00° and 29.60°C, 10.05° and 13.75°C, and 65.50 and 58.25 per cent, respectively. The correlation studies further established that rising maximum and minimum temperatures from 21.70° to 32.90°C and 6.20° to 14.10°C, respectively and the declining relative humidity from 81.00 to 58.25 per cent favoured the population build-up of this pest. The regression analysis showed that the weevil population was more dependent on the weather factors prevailing intimately during the period of its activity rather than one or two weeks earlier. The coefficient of determination factor (R²) values showed that prevailing temperature and relative humidity jointly accounted for more than 46.00 per cent fluctuation in the pest population.