Influence of weather factors on population build-up of pod fly, Melanagromyza obtusa Malloch, in main season pigeonpea grown under conditions of North Bihar (India)*

Incidence of pod fly (Melanagromyza obtusa Malloch.) infesting main season pigeonpea cv. Bahar, was studied in relation to two weather factors, viz, ambient temperature and relative humidity during 1990–91 and 1991–92 crop seasons. The results revealed that the pest started its activity in the first week of January with mean population around 0.67 and 0.43 larvae/plant in the first and second year, respectively. In both the crop seasons, it maintained its activity till March end when the crop matured. The mean population of M. obtusa on pooled basis showed an increasing trend from 10.93 to the peak of 35.27 larvae/plant during the period from Janury end to March beginning, when the average maximum and minimum temperatures ranged from 24.20° to 27.55°C and 8.85° to 12.55°C, respectively with the average relative humidity fluctuating between 65.5 and 79.5 per cent. With the rising mean temperature above 21.68°C and the fall in average relative humidity below 58.28 per cent, the pest population started declining from the second week of March and ultimately reached its minimum level (0.89 larvae/plant) by the last week of March, when the mean temperature and relative humidity fluctuated around 26.9S°C and 52.5 per cent, respectively. The correlation and regression studies could not establish any relationship between the population build-up of M. obtusa and these two weather factors.