Effects of Fipronil and Lambda-Cyhalothrin on Foraging Intensity of Syrphid Episyrphus balteatus in Onion Crop

The study evaluated the effect of two commonly used insecticides, fipronil and lambda-cyhalothrin, on the foraging behaviour of Episyrphus balteatus on onion blooms under field conditions. Foraging behaviour was assessed via the foraging speed, foraging rate and foraging intensity on the basis of the insect count at regular intervals up to 14 days after spray. The results revealed significant variation in foraging behaviour among the treatments. Overall, the foraging speed was lowest in fipronil-treated plots (7.9 sec flower ^-1), followed by lambda-cyhalothrin (8.1 sec flower^-1), whereas the control plots presented the highest foraging speed (10.8 sec flower^-1). Foraging rate was highest in the lambda-cyhalothrin-treated plots (7.8 flowers min^-1), followed by the fipronil-treated plots (7.6 flowers min^-1), whereas the control plots presented the lowest rate (6.1 flowers min^-1). In fipronil-treated plots, significant suppression of foraging intensity persisted until the 7^thday after spray, whereas in lambda-cyhalothrin-treated plots, it persisted until the 5^th day.