Effect of insecticides on foraging behaviour and pollination role of Apis mellifera L. (Hymenoptera: Apidae) on toria (Brassica campestris var. toria) crop

Abstract

The effects of insecticide application on foraging and pollination by honeybees in toria (Brassica campestris var. toria) cultivar RSPT-1 were studied at Jammu (India).Under field conditions the application of betacylfluthrin, betacyfluthrin + imidacloprid and carbaryl resulted in 100% bee mortality within one hour of spraying. After 48 hours, 100% mortality was recorded in all the treatments except malathion (94%). The post-spraying effects of the insecticides were much higher during the first hour after treatment, but after 48 hr there was 100% mortality in all treatments except imidacloprid (43%). Residual effects after spraying were high for flowers sprayed with imidacloprid (76% mortality), demeton-o-methyl, carbaryl, and ethiprole, moderate for betacyfluthrin (49%), betacyfluthrin + imidacloprid, and profenophos, and low for malathion (12%). The residual effect decreases with time and after 96 hours of spraying, the residual effect was reduced in almost all the insecticides. The number of foraging bees were greatly reduced in all treatments 24 hr after spraying, compared to levels before spraying, recovering considerably after 3 days, and normal after 7 days. Open pollination resulted in 1.80 times more yield compared to caged condition and crop pollinated by bees alone. This study suggests that both protective application of insecticides and use of honeybees for pollination are essential for maximum crop yields.