Bio-pesticide applications may impair the pollination services and survival of foragers of honey bee, Apis cerana Fabricius in oilseed brassica

Abstract

Honey bees and brassica plants are co-evolved and due to the peculiar floral characters, mustard (Brassica juncea) plants are strongly dependent on bees for survival. Mustard is one of the most important oilseeds across the world. Insect pests often cause huge economic losses in mustard and their management, especially during flowering stage is very crucial to achieve maximum yield, although this step often displays undesirable effects on the foraging bees. Effects of synthetic pesticides on bees are widely documented and extensively reported. Although the numbers of pesticides/bio-pesticides are widely used in oilseed brassica's, the reports are mostly focused on neonicotinoids. To identify the bee-friendly pesticides, the study was conducted in two tier approach (i.e. laboratory and field conditions) and determined the potential impacts of widely used biopesticides on Asiatic honey bees, Apis cerana Fabricius. The LC50, LC90 and LD50 were determined for four destructive pests and honey bees, to assess their risk against honey bees. In laboratory studies, LC50's of pesticides to the honey bee was in the order ofBeauveria bassiana 1.5L (4.79%) > Bacillus thuriengiensis 8SP (1.67%) > Azadirachtin 0.03 EC (1.64%) > Annonin 1 EC (1.22%) > Spinosad 2.5 SC (0.006%) > Imidacloprid 17.8SL (0.005%). Based on three essential risk assessment criteria's (viz., Selectivity ratio, Probit substitution method (%) and Hazard Ratio/Risk quotient); the Azadirachtin, Anonnin, B.bassiana and Bt var. k were found selective, and slightly to moderately toxic to the honeybee; whereas Spinosad and Imidacloprid was found non-selective and dangerous to the bees. Entomopathogenic fungus, Nomuraea rileyi was found absolutely harmless to the bees. In field studies, the relative abundance, foraging rate and foraging speed of honey bees was significantly affected in different treatments even up to 2 days of spraying. Among bio-pesticides, deterrence/repellent effect was, however, strongly observed in Annonin and Spinosad treatments. Significantly higher yield was obtained in Azadirachtin (1.43 t/ha) and Anonin (1.22 t/ha) treated plots. Except Spinosad, remaining bio-pesticides were found selective to the foraging bees, nevertheless considering the efficiency in pest control and higher yield, Azadirachtin 0.03 EC and Annonin 1 EC could be efficiently used in Integrated Pest cum Pollinator Management Programme (IPPM) in oilseed brassica's. The spraying of Spinosad may be discouraged, especially at flowering time.