Need for growing non-Bt cotton refugia to overcome Bt resistance problem in targeted larvae of the cotton bollworms, Helicoverpa armigera and Pectinophora gossypiella

Muhammad Rafiq Shahid,Abid Mahmood,Muhammad Shakeel,Muhammad Farooq,Zia Ullah Zia,Misbah Ashraf,Saghir Ahmad

doi:10.1186/s41938-021-00384-8

Abstract

BackgroundThe effectiveness of Bacillus thuringiensis (Bt) cotton against target arthropod larvae is decreasing day by day. The comparative effect of Bt expression among Bt cotton varieties and different plant parts was observed against the cotton bollworms: Helicoverpa armigera and Pectinophora gossypiella larvae.ResultsIn the present study, larval mortality of H. armigera was higher than P. gossypiella among selected Bt cultivars. 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. armigera of FH-142, MNH-886, IR-3701, and FH-Lalazar, respectively. These values depicted that P. gossypiella had more Bt resistance problem than H. armigera larvae. The host range of both targeted insect larvae was different from each other due to the polyphagous feeding nature of the larvae of H. armigera that feed on different host plants, but P. gossypiella attacked only cotton with monophagous feeding habit. It was also notable from results that Bt expression 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.ConclusionsIt was concluded that farmers be advised to follow the practice of growing non-Bt as a refuge crop to reduce the problem of Bt resistance in the target arthropod species.

Highlights

The effectiveness of Bacillus thuringiensis (Bt) cotton against target arthropod larvae is decreasing day by day
Insecticidal crystalline protein intensities and their effectiveness depend upon the cultivar’s potential to produce Bt protein, its growth stage, and plant part used (Olsen et al 2005 and Wan et al 2012). It influences the biological parameters of feeding insect species because the life parameters of herbivores depend on the Shahid et al Egyptian Journal of Biological Pest Control (2021) 31:39 stage of larvae and the quantity of Cry1Ac ingested by it (Stewart et al, 2001)
The highest Bt toxin level of Cry1Ac protein was quantified in IR-3701 (1.5 μg/g), followed by FH-142 (0.87 μg/g), MNH-886 (0.39 μg/g) and FH-Lalazar (0.31 μg/g) (Fig. 1)

Summary

Introduction

The effectiveness of Bacillus thuringiensis (Bt) cotton against target arthropod larvae is decreasing day by day. Owing to continuous cultivation of Bt cotton and restricted feeding only on cotton, the field population of monophagous larvae has more chances of evolved resistance against the Cry1Ac protein (Tabashnik et al, 2013; Jin et al, 2015 and Sansinenea 2019). In this way, P. gossypiella seems to become a more damaging insect pest of cotton than the polyphagous H. armigera (Dhurua and Gujar, 2011)

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Results

Conclusion