author(s)
PP Pradhan, RN Borkakati and DK Saikia

abstract
Field experiment was conducted to study the seasonal incidence of insect pests and natural enemies revealed that aphid (L. erysimi), flea beetle (P. cruciferae) and sawfly (A. lugens proxima) were appeared during 51^st SMW i.e. 3^rd week of December, 2018 while the natural enemies viz., ladybird beetle (C. transversalis) and D. rapae appeared during 4^th SMW i.e. (last week of January, 2019). The correlation studies between different weather parameters and population of major insect pests revealed that maximum temperature recorded positive correlation with aphid, flea beetle and sawfly with correlation coefficient, r= 0.502, r= 0.510 and r= 0.461, respectively.In case of natural enemies observed in mustard field, maximum temperature had a positive impact on C. transversalis (r= 0.195) and D. rapae population (r= 0.194). Minimum temperature had non-significant positive correlation with aphid (r= 0.456) and flea beetle (r= 0.120) population but had a significant negative correlation with sawfly population (r= -0.625) and significant positive correlation with ladybird beetle (r= 0.669) and D. rapae population (r= 0.682). Morning relative humidity had non-significant negative correlation with all the insect pests observed in mustard crop except aphid where it was found to be significant (r= -0.606). Evening relative humidity had non-significant negative correlation with aphid (r= -0.251), flea beetle (r= -0.484) and sawfly (r= -0.525) population and in case of natural enemies viz., C. transversalis (r= -0.058) and D. rapae (r= -0.047) also it was found to be negatively correlated. Rainfall had positive and non-significant correlation with aphid (r= 0.038), C. transversalis (r= 0.066) and D. rapae (r= 0.080) population but it had negative and non-significant correlation with flea beetle (r= -0.206) and sawfly population (r= -0.552).