Growth and molting disruption effects of azadirachtin against Drosophila melanogaster (Diptera: Drosophilidae)
Radia Bezzar-Bendjazia, Samira Kilani-Morakchi, Nadia Aribi
Azadirachtin, a biorational insecticide, known to be an antagonist of the juvenile hormone and 20 hydroxyecdysone (20E), has been used successfully against insect pests; however, its effects on non-target organisms remain contradictory. The current study examined the lethal and sublethal effects of azadirachtin on Drosophila melanogaster Meigen, 1830 (Diptera: Drosophilidae) as biological model. Azadirachtin was applied topically at two dose LD25 (0.28 μg) and LD50 (0.67 μg) on early third instar larvae. Treatment reduced, significantly pupation and eclosion rates. The increase of doses was directly proportional to reduction in adult emergence. Indeed, pupation rate of 93.33% in controls series drop to 81.33% and 76% respectively for LD25 and LD50. The eclosion rates is significantly reduced, after azadirachtin treatment, as compared to controls (93.33%) and the value recorded are 72% and 46.66%, respectively for LD25 and LD50. In addition, azadirachtin exhibited various morphological abnormalities on larvae, pupae and adult stages (heavy pigmentation of larvae, pupa-adult intermediate, incomplete/malformed adults), the value recorded was about 13.5 to 27% higher than the controls. Finally, results showed that the compound reduced, at the two tested doses, the body weight of all developmental stages of D. melanogaster (larvae, pupae and adults) about 10 to 20%. Thus, our results suggested that a topical application of azadirachtin to early third instar larvae interfered with the endocrine events and disrupted the normal development of this insect. Consequently, this reduced-risk insecticide should be used with caution in integrated pest management programs (IPM).