Groundnut pest complex: 4. Regression studies to determine the associationship between jassid and thrips and weather parameters

Regression studies revealed the close relationship between population build up of pests and weather parameters Empoasca kerri Pruthi and Caliothrips indicus Bagnall had a negative association with the minimum daily temperature (except in groundnut intercropped with sorghum), relative humidity, rainfall and wind speed (in summer only). While maximum daily temperature, sunshine had a positive bearing on the occurrence of jassid and thrips in groundnut as a sole crop and groundnut intercropped with red gram, green gram, sorghum, soybean and sesamum. This explains the finding that during summer, the number and density of jassid and thrips were as lower as compared to the kharif seasons. The comparatively drier kharif of 1987 minimized the occurrence and density of these two pests as compared to kharif, 1988. Multiple linear regression modelling brought out a significant effect of at least one of the weather parameters in the case of E. kerri Pruthi and C. indicus. The groundnut jassid decreased by 0.5 insects per plant when the minimum daily temperature was increased by one unit. Hence, this pest was therefore observed in higher proportions on the initial stages of the crop growth in summer 1988, when the minimum daily temperature was low. Whereas C. indicus population decreased by 0.2 and 0.1 per plant, respectively with one unit increase of minimum daily temperature and relative humidity during kharif, 1987.