Status of defender and offender arthropods in Bt transgenic cotton

Abstract

The widescale cultivation Bt cottons in India has altered the landscape of pest management, particularly of sap feeders. To have updated understaning field surveys were carried out during kharif 2022-23 and arthropod defenders (spiders, coccinellids and chrysopids) and offenders (sucking pest) in Bt cotton at Dharwad and Haveri districts of Karnataka were noted. Their peak activity was found during flowering stage. In the defenders, spiders exhibit a higher abundance compared to chrysopids and coccinellids. Thrips, conversely emerged as predominant offender. In Dharwad district, seasonal mean of spider was 1.23/plant. Chrysopids displayed a seasonal mean of 0.96 individual 1.48 spiders/ plant were recorded, chrysopids exhibited a seasonal mean of 1.33 individuals/plant and coccinellids 1.36/plant. Offenders displayed specific seasonal incidences, with thrips recorded at 14.97/3 leaves, leaf hoppers at 2.67/3 leaves, aphids at 17.05/3leaves, and whiteflies at 1.27/3 leaves. Notably, offender defender ratios differed, with Dharwad district at 7.5 offender per defender and Haveri district at a slightly lower ratio of 6.5 offender per defender was recorded. Overall higher offender and defender population was observed at Haveri district. Thus it’s important to maintain wider ratio of defender: offenders through selective practices.