Seasonal incidence of key natural enemies of onion thrips, Thrips tabaci Lindeman and their interaction with weather parameters on onion crop in Terai region of Uttarakhand, India

Abstract The purpose of this study was to determine the seasonal incidence of important natural enemies of onion thrips, Thrips tabaci. Under natural conditions, healthy onion seedlings were transplanted, and to determine the number of natural enemies, the crop was observed on a weekly basis. The population of spiders feeding on thrips was observed from the first appearance until crop harvesting in both the years, and it was found peaking in the last week of April in the first year and the second week of May in the second year. Similarly, coccinellids were first found in the first and second weeks of April in the first and second years, respectively, and were active throughout the growth period, peaking in the last week of April in the first year and the first week of May in the second year. Orious bugs were also recorded from their first arrival and were found with a peak in the third week of April in the first year and the last week of April in the second year. Maximum and minimum temperatures, rainfall in the first year, and sunshine hours in the second year all had a significant positive effect on the spider population feeding on onion thrips; however, morning relative humidity and evening relative humidity in the second year had a significant negative effect. The maximum temperature in the second year, the minimum temperature, and the rainfall in the first year all had a significant positive effect. However, morning relative humidity and evening relative humidity in the second year only had a significant negative influence on the coccinellid population. The maximum and minimum temperatures and sunshine hours had a significant positive effect on the orious bug population; however, morning relative humidity and evening relative humidity showed a significant negative effect.