Effect of a Bt-based product (Vectobar) on esterases and phosphatases from larvae of the mosquito Aedes aegypti

Abstract

Bacillus thuringiensis (Bt)-based formulations possess potent insecticidal property, and they are being used in insect vector control programs all over the world. In this study, we examined the efficacy of a Bt-based product (Vectobar) on two developmental stages (fourth instar larvae and pupae) of the mosquito Aedes aegypti. Vectobar at a concentration of 0.25ppm was found to inflict 100% mortality of fourth instar larvae of A. aegypti within 24h. By contrast, this Bt-based product tested up to 2ppm was not effective against the pupae of A. aegypti. The systemic effect of Vectobar was further assessed in the fourth instar larvae of A. aegypti by measuring the levels of total proteins and activity of two important marker enzymes: esterases and phosphatases. Exposure of the larvae to Vectobar at a lethal threshold concentration (0.05ppm) significantly decreased the level of total protein (34%) as well as the activities of acetylcholinesterase (36%), α-carboxylesterase (34%) and alkaline phosphatase (49%). On the other hand, 40% increase in the level of acid phosphatase activity was recorded in these larvae. The Vectobar did not affect the level of β-carboxylesterase activity in the larvae of A. aegypti. This investigation clearly demonstrates differential modulation in the activities of esterases and phosphatases in Vectobar exposed larvae of A. aegypti.