Weather based forecasting model for emergence of Aprostocetus purpureus (Cameron) – a parasitoid of lac insect, Kerria lacca (Kerr)

Indian lac insect, Kerria lacca is a scale group beneficial insect which suffers by several natural enemies. The establishment of the relationship between the incidences of natural enemies on lac insects with weather variables is essential for formulating management strategies well in advance. The relationship between weather factors and the emergence of A. purpureus was studied from 2011–12 to 2020–21 on the rangeeni summer (baisakhi) lac crop. Correlation and regression analyses were done after pooling ten years data (2011-12 to 2020-21) during the critical lac growth period i.e. SMW 8 to SMW 20. The relative abundance of lac-associated fauna showed that three parasitoids ((Aprostocetus purpureus, Tachardiaephagus tachardiae, and Tyndarichus(=Parechthrodryinus) clavicornis)) and one predator (Eublemma amabilis) were abundant. Among them, A. purpureus recorded maximum percent infestation, which was 84% and 75% on ber and palas, respectively. Maximum number of A. purpureus was emerged during the sexual maturity period (8 to 20 SMW) of the summer lac crop. The incidence exhibited a significant negative correlation with maximum (Tmax) and minimum temperature (Tmin) and a significant positive correlation with morning and evening relative humidity (RH-II).  Stepwise regression analysis showed Tmax and RH-II were the most important factors contributing to 68% variation in the incidence of A. purpureus on palas. The present study results indicated that environmental factors played a significant role in the incidence of parasitoids on lac insect.