Assessment of toxicity of bio-pesticides to the Indian honey bee, Apis cerana indica (Fabricius) in oilseed Brassica
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Date
2018-10
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College of Post Graduate Studies in Agricultural Sciences, Central Agricultural University , Imphal
Abstract
Rapeseed and Mustard is the second most important edible oilseed crop in India after Soybean and accounts for 27.8 per cent of the total oilseeds produced in the country.The crop shares around one-third of the India's oil production, making it the country’s key edible oilseed crop. It is an open pollinated crop which is heavily pollinated by honey bees. Recently declines of various pollinators have been reported. Biopesticides are the integral part of the organic agriculture and they are considered to be safe to the natural enemies and pollinators. However, several studies indicated that bio-pesticides may also be harmful to the pollinators. It is essential to assess the risk of bio-pesticides to the foraging honey bee in oilseed brassica to promote higher yield with efficient pest control. Therefore, commonly used bio-pesticides were evaluated for their safety to the Indian honey bee, Apis cerana indica (Fabricius). The study was conducted in two tier approach i.e. laboratory and field conditions. For in vitro studies, target insects were collected from entomology farm at ICAR-NEH, Umiam and reared according to standard protocols. LC50, LC90 and LD50 values were determined for the insect pests and honey bees, to assess the risk against honey bees. Laboratory studies showed that LC50’s of pesticides to the honey bee was in the order of Nomuraea rileyi (100) > B. bassiana (4.798) > Bt var k (1.670) > azadirachtin (1.642) > annonin(1.221) > cyantraniliprole (0.056) > spinosad (0.006) > imidacloprid (0.005). Acute toxicity data of insect pests and honey bee were used to determine three essential risk assessment criteria’s viz., selectivity ratio, probit substitution method (%) and hazard ratio/risk quotient. Based on these three risk assessment criteria’s, azadirachtin, annonin, B. bassiana and Bt var kurstaki were found selective, but slightly to moderately toxic to the honeybee; whereas, spinosad, cyantraniliprole and imidacloprid were found non-selective and dangerous to the bees. N. rileyi was found selective and absolutely harmless to the bees. Relative abundance, foraging rate, foraging speed and yield in different treatments were considered to know the influence of biopesticides on foraging activity in vivo. Relative abundance, foraging rate and foraging speed of honey bees were significantly affected in different treatments even up to 2 days of spraying. Among bio-pesticides, deterrence/repellent effect was however severely observed in annonin and spinosad treatments up to 2 days. Significantly higher yield was obtained in azadirachtin (1.43 t/ha) and annonin (1.22 t/ha) treated plots. This study concludes that, except spinosad remaining bio-pesticides were safe to the foraging bees, however considering efficient pest control and higher yield, the neem oil based formulation of azadirachtin and annonin could be efficiently used in Integrated Pest and Pollinator Management Programme (IPPM) in oilseed brassica’s. Owing to its harmful effect on bees, use of spinosad 2.5 SC should be discouraged especially during the flowering period in oilseed brassica