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The objective of the present study was to investigate the effect of chewing pests on Bt and Non-Bt cotton varieties in Southern Punjab (Pakistan). Five cotton varieties (One NIAB Non-Bt and four Bt varieties viz. IUB-33, MNH-988, Lalazar, and Sitara-009) were grown in four regions (Multan, Khanewal, Muzaffar Garh and Kabirwala). These cotton varieties were surveyed for the collection of data on different chewing pests (American, Pink, and Spotted bollworms) populations. The eggs and adult counts were calculated from April 2014 to October 2016. It was found that NIAB Non-Bt cotton has resulted in a larger number of chewing worms and eggs as compared to Bt varieties. Bt cotton showed significantly higher resistance than Non-Bt variety against chewing bollworms. It may be due to a lesser number of adults and eggs of these bollworms. However, it was estimated that these varieties were also affected by the climatic conditions of southern Punjab in Pakistan. Also, Non-Bt cotton varieties showed poor Host plant susceptibility index (HPSI) as compared to Bt varieties for all four sites. Host plant susceptibility index (HPSI) for Non-Bt cotton variety was 47.5, 40.59, and 25.1, on the other hand (HPSI) for Bt varieties were 90.18, 94.81 and 97.82 respectively for years 2014-2016. Therefore, it was suggested that the Bt cotton varieties are better than Non-Bt cotton varieties due to greater resistance against chewing bollworms.
Keywords: Bt cotton; Chewing worms; Climate; HPSI (Host Plant Susceptibility Index); Non-Bt cotton; Resistance