Abstract
Transgenic Bt cotton with genes from soil inhabiting spore forming bacterium Bacillus thuringiensis Berliner produces δ-endotoxin for the control of lepidopteran insects. The prey-mediated effects of Cry protein on the third trophic level is the most realistic exposure pathway that needs to be addressed as an important component of environment risk assessment. The green lacewing, Chrysoperla zastrowi sillemi (Esben-Petersen) (Neuroptera: Chrysopidae) is the most important generalist predator in the cotton ecosystem in India. The tri-trophic interactions involving Bt cotton expressing single (Cry1Ac) and dual toxins (Cry1Ac and Cry2Ab) fed herbivores, i.e. mealybug, Phenacoccus solenopsis Tinsley, whitefly Bemisia tabaci (Gennadius) and leafhopper, Amrasca biguttula biguttulla (Ishida) on the fitness of C. zastrowi sillemi, were studied. The development, survival and body weight of C. zastrowi sillemi had no deleterious effect as there were insignificant differences in any of the studied fitness parameters regardless of having consumed prey fed on Bollgard, Bollgard II and non-Bt cotton plants. The feeding potential of C. zastrowi sillemi on mealybug was also not different on Bt or non-Bt cotton plants. ELISA studies confirmed the presence of Cry proteins in Bt cotton leaves; however, no Cry1Ac or Cry2Ab protein was detected in prey herbivores (P. solenopsis, B. tabaci and A. biguttula biguttula) or in the predator C. zastrowi sillemi. It could be concluded that transgenic cotton that expresses single (Cry1Ac) or dual (Cry1Ac and Cry2Ab) toxins had no apparent effect on the fitness of the predator through its preys P. solenopsis, B. tabaci and A. biguttula biguttulla.
Highlights
Modified cotton with genes from soil inhabiting spore-forming bacterium Bacillus thuringiensis Berliner (Bt) produces δ-endotoxin, which is lethal to many lepidopteran pests
The objectives of the study were (1) to quantify the impact of cotton cultivars expressing single toxin (Bollgard; Cry1Ac), dual toxins (Bollgard II; Cry1Ac + Cry2Ab) and non-toxin on the survival, development, and body weight of the predator C. zastrowi sillemi through non-target sucking insect pests; (2) to study the predatory potential of the predator when fed on cotton mealybug P. solenopsis reared on Bt cotton; and (3) to study whether Cry1Ac and Cry2Ab proteins can pass via the food chain to the third trophic level
Development, survival and weight of C. zastrowi sillemi fed on P. solenopsis reared on Bt and non-Bt cotton leaves Different life parameters, i.e. larval period (F = 0.01; df = 2.70; P = 0.994), pupal period F = 0.08; df = 2.60; P = 0.927) and adult longevity (F = 0.01; df = 2.60; P = 0.987) of C. zastrowi sillemi did not differ when fed on P. solenopsis reared on Bollgard or Bollgard II or non-Bt cotton leaves (Table 1)
Summary
Modified cotton with genes from soil inhabiting spore-forming bacterium Bacillus thuringiensis Berliner (Bt) produces δ-endotoxin, which is lethal to many lepidopteran pests. The area planted under biotech upland cotton globally in 2017 was 24.1 million hectares, India, having the largest area. In India, the area under Bt cotton has increased from 50,000 ha in 2002 to 11.4 million hectares in 2017, representing an unprecedented 227-fold jump in 16 years (James 2017). Studies conducted in Australia, USA, China and India have indicated that the Cry proteins in transgenic Bt cotton are available throughout the cropping season with temporal and spatial variations (Kranthi et al 2005 and Shera and Arora 2016). At the third trophic level, predators and parasitoids may get exposed to Cry proteins, when they feed on herbivores that have consumed plant tissues having Bt protein (Torres et al 2006; Mota et al 2012; and Kumar et al 2014). Exposure on the third trophic level through prey is the most realistic exposure pathway that needs to be addressed as an important component of environment risk assessment
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