| Abstrakt: |
Background: The effectiveness of Bacillus thuringiensis(Bt) cotton against target arthropod larvae is decreasing day by day. The comparative effect of Btexpression among Btcotton varieties and different plant parts was observed against the cotton bollworms: Helicoverpa armigeraand Pectinophora gossypiellalarvae. Results: In the present study, larval mortality of H. armigerawas higher than P. gossypiellaamong selected Btcultivars. Median lethal concentration (LC50) values were 8.91, 13.4, 14.0, and 36.4 for P. gossypiella, while 5.91, 4.04, 2.37, and 8.26 for H. armigeraof FH-142, MNH-886, IR-3701, and FH-Lalazar, respectively. These values depicted that P. gossypiellahad more Btresistance problem than H. armigeralarvae. The host range of both targeted insect larvae was different from each other due to the polyphagous feeding nature of the larvae of H. armigerathat feed on different host plants, but P. gossypiellaattacked only cotton with monophagous feeding habit. It was also notable from results that Btexpression in reproductive parts where the attacked pink bollworm was lower than the American bollworm, so the former had the maximum chance of resistance due to repeated exposure to Bt. Conclusions: It was concluded that farmers be advised to follow the practice of growing non-Btas a refuge crop to reduce the problem of Btresistance in the target arthropod species. |
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