Detection of pesticide and their effects on silkworm, Bombyx mori L. (Lepidoptera: Bombycidae)

Abstract

Abstract Background Non-spinning of cocoon and mortality in silkworm due to pesticides exposure has become a threat for sericulture industry in India. The effect of pesticide on silkworm and Acetylcholinesterase, one of the main targets for insecticides, was studied for symptoms and quantitative analysis by screening insecticides other than organophosphates and carbamates. Results Insecticide exposure to silkworms resulted in vomiting, flaccid body, rectal protrusion, chain faeces, body shrinkage, partial and non-spinning and mortality. The probit analysis showed the pesticide concentration in ≥ 0.9 µg/mL led to mortality, 0.025–0.0012 µg/mL led to non-spinning and ≤ 0.0006 µg/mL led to spinning of cocoon. Studies employing spectrophotometer at 412 nm showed Imidacloprid had highest inhibition on activity of AChE extracted from silkworm head. We also studied the effect of pesticides on commercially available AChE, and the results found that Anthranilic diamides, pyrethroid and fungicides also inhibited AChE in time-dependent spectrophotometric analysis. Further, a rapid visual screening paper-strip method for semi-qualitative detection of pesticides on mulberry leaf and soil was standardized using AChE (1.25 µL of 1000 U/mL) and indoxyl acetate (10 µL of 10 mM) on Whatman filter paper 1. To validate, 62 field samples were tested from Karnataka, Tamil Nadu, Andhra Pradesh and Kerala, of which 35 samples were found positive for pesticide and 27 samples were negative. Conclusion These results indicate that the pesticide exposure has resulted in silkworm toxicity, and AChE can be employed as biomarker for pesticide toxicity study.

Keywords

• Silkworm
• Paper strip
• Pesticide
• Non-spinning
• Mortality
• Acetylcholinesterase