Toxicological Effect of Insecticides on Bactrocera zonata (Saunders) (Diptera, Tephritidae) Life Parameters

The peach fruit fly, Bactrocera zonata (Saunders), is a destructive pest affecting a variety of fruit crops. This study evaluated the toxicity of seven insecticides Radiant, Malathion, Trichlorfon, Fenoxycarb, Lufenuron, Bifenthrin, and Methomyl against B. zonata larvae and pupae using surface contact and sandy soil treatment methods under laboratory conditions. Radiant was the most toxic to full-grown larvae in surface contact treatment (LC₅₀ = 5.60 ppm), while Malathion showed the highest toxicity to 1-day-old pupae (LC₅₀ = 71.99 ppm). Fenoxycarb exhibited superior performance in sandy soil, with the lowest LC₅₀ values for both larvae (39.04 ppm) and pupae (145.02 ppm). Toxicity indices and slope values further supported the efficacy ranking. Morphogenetic abnormalities including malformed wings, incomplete emergence, and larval-pupal intermediates were observed across treatments, especially in those with Fenoxycarb, Lufenuron, and Methomyl. Biological assessments showed that all insecticides adversely affected reproductive parameters, including fecundity, hatchability, and sterility. Malathion resulted in the longest oviposition period and highest hatchability, while Radiant led to the highest female sterility (87.85%). Adult longevity was significantly reduced by fenoxycarb and methomyl treatments. Overall, Radiant and Malathion demonstrated high larvicidal and pupicidal activity via surface contact, while Fenoxycarb and Lufenuron were most effective in sandy soil applications. These findings support the integration of specific insecticides into B. zonata management programmes, particularly those targeting the immature stages in both above-ground and soil environments.