DEVELOPMENT AND MECHANISMS OF RESISTANCE IN PEACH FRUIT FLY Bactrocera zonata (SAUNDERS) TO MALATHION, LAMBDA-CYHALOTHRIN AND SPINOSAD

Abstract

The first part of the present study was undertaken to investigate the potential of peach fruit fly, Bactrocera zonata, to develop resistance to malathion, lambda-cyhalothrin and spinosad under laboratory conditions and the possible mechanisms of resistance. Three resistant strains were established; the malathion-resistant strain (M-R) (Resistance ratio (RR): 52-fold after eight generations of selection), the lambda-cyhalothrin-resistant strain (L-R) (RR: 12-fold after six generations of selection) and the spinosad-resistant (S-R) (RR <3-fold after six generations of selection). The L-R and S-R strains did not show cross-resistance to malathion. The selected strains were more tolerant to methomyl and deltamethrin, and more susceptible to dimethoate, lambada-cyhalothrin and spinosad. Piperonyl butoxide (PBO) had no synergistic effects for malathion and spinosad, while it increased the toxicity of lambda-cyhalothrin in both susceptible and L-R strains; and the synergistic effect was higher in L-R strain. Biochemical analysis revealed that esterase activity in the M-R strain was higher than that in the susceptible strain; these differences were significant in the eighth generation and in females of the sixth generation. There were no significant differences in esterase activity between the L-R and S-R strains and the susceptible strain. No significant differences in acetylcholinesterase (AChE) activity were found among males of all studied strains. However, significant differences were found between females of the third generation of the M-R and S-R strains and females of the susceptible strain. Glutathione-S-transferase (GST) activity was higher in all resistant strains than in the susceptible strain. The highest significant activity was recorded in the eighth generation of M-R. Cytochrome P450 activity in females of the third and eighth generations of the M-R strain and the third generation of S-R strain was significantly lower than that in the susceptible strain. Activity in females of the sixth generation of the L-R strain was significantly higher than that of susceptible strain. Sequencing study of B. zonata AChE cDNA revealed that the two mutations I214V and G488S, which are responsible for acetylcholinesterase insensitivity in some Bactrocera species, were missing in the M-R strain. The second part of this study was undertaken to evaluate the efficacy of cover spray of Malathion Adwia 57% EC and Halothrin N 5% EC and bait spray of Conserve 0.024% CB against fruit flies in guava orchard in El-Beheira Governorate, Egypt. Throughout the experiment, peach fruit fly was absent from ammonium acetate traps and samples of infested fruits. Only the Mediterranean fruit fly was found. The cover spray treatment of Halothrin N 5% EC was the most effective with the lowest percentage of infested fruits and the highest reduction in infestation. The cover spray treatment of Malathion Adwia 57% EC was the least effective with the highest percentage of infestation and the lowest reduction in infestation. The bait spray of Conserve 0.024% CB did not provide sufficient protection against fruit fly infestation, and caused 54.4% reduction in infestation during the experimental period compared to 46.9 and 68.2% in the treatment of Malathion Adwia 57% EC and Halothrin N 5% EC, respectively.