Insecticidal Activity of Carbaryl and its Mixture with Piperonylbutoxide Against the Red Palm Weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) and their Effects on Acetylcholinesterase Activity

The insecticidal activity of carbaryl alone and its mixture with Piperonylbutoxide (PBO) was tested against males, females and larvae of the Red Palm Weevil (RPW), Rhynchophorus ferrugineus (Olivier), by both the feeding and the topical application methods. In addition, the Acetylcholinesterase (AChE) activity, the in vitro effect of carbaryl alone and the in vivo effects of carbaryl, PBO and their mixture on the AChE activity were estimated in RPW. A modification was carried out to enable estimation of AChE activity in this destructive pest. Tested materials were more toxic by feeding than by topical application and larvae were more susceptible than adults. In case of food treatment, the LC₅₀ values of carbaryl alone were 1.183, 1.43 and 0.0367% for males, females and larvae, respectively. PBO had great synergistic effect on carbaryl toxicity, the LC₅₀ values for carbaryl+PBO were 0.0155, 0.0253 and 0.00556% against males, females and larvae, respectively. The topical LD₅₀ values for carbaryl and carbaryl+PBO against larvae were 27.1 and 14.4 μg/larva, respectively. The inhibition percentages of AChE activity in larvae fed on carbaryl and (carbaryl+PBO)-treated sugarcane were 0.8 and 64.4%, respectively. The results indicated the great role of oxidases in the reduction of carbaryl toxicity and their inhibition by PBO.