Assessment of selectivity of insecticides against hymenopteran egg parasitoids (Telenomus dignus G. and Trichogramma japonicum A.) of yellow stem borer (Scirpophaga incertulas W.) in Kharif rice

The compatibility of insecticides with hymenopteran egg parasitoids (natural enemies), viz. Telenomus dignus and Trichogramma japonicum of yellow stem borer (Scirpophaga incertulas) in kharif rice (Oryza sativa) was investigated in Purba Bardhaman district of West Bengal during 2022–23. A total of seven chemical insecticides were chosen for the experiment along with one control treatment where only water was sprayed. The field design was set up with a randomised block design (RBD) with eight treatments in three replications. A few parameters were studied in this experiment and those were parasitism rate of eggs in egg masses (%), parasitism reduction (%), parasitic potential (%), adult emergence (%), emergence reduction (%) and selectivity classification of applied insecticides based on parasitism reduction. From the results of the experiment, it was observed that, for the above mentioned first four parameters which were found effective for the three insecticides like Thiamethoxam + Chlorantraniliprole, Tetraniliprole and Chlorantraniliprole and other chemicals were not so effective for the first four parameters. From the selectivity classification of insecticides, it was found that the three chemical treatments (Thiamethoxam + Chlorantraniliprole, Tetraniliprole and Chlorantraniliprole) fall under the harmless class (parasitism reduction < 30 %) while the rest of the other chemicals came under the slightly harmful class (30 % ≤ parasitism reduction ≤ 79 %) for T. dignus as well as for T. japonicum. The results highlight the compatibility of selected chemicals with biological control agents and their incorporation into integrated pest management (IPM) programmes with minimum non-target effects in the rice ecosystem.