Comparative toxicity of three ecdysone agonist insecticides against the Mediterranean flour moth

The Mediterranean flour moth, Ephestia Kuehniella Zeller (Lepidoptera: Pyralidae), is an important pest in stored products worldwide, and is one of the major pests in flour mills in Algeria. Because environmental consideration, alternative approaches to neurotoxic insecticides, as well as safe, effective, and sound integrated pest management strategies are developed pest control agents such as the insect growth regulator (IGRs). Among these IGRs, the bisacylhydrazine derivatives are nonsteroidal ecdysterold agonists that mimic the action of moulting hormones and induce a precocious and incomplete moult in several insect orders. In topical bioassays using the pupae of E. kuehniella, three ecdysteroid agonists: RH-5849, the first bisaclhydrazine ecdysone agonist and two analogs, RH-5992 (tebufenozide) and RH-0345 (halofenozide), were evaluated on the reproduction under laboratory conditions. In a first series of experiments, the efficacy of these compounds was tested. These compounds exhibited insecticidal activity and the duration of pupal development was reduced with a dose-response relationship. Among the three tested compounds, tebufenozide (LD50 = 0.005 microg) appeared the most potent ecdysteroid agonist against E. kuehniella (RH-5849: LD50 = 0.05 microg and RH-0345: LD50 = 5.10 microg). In a second series of experiments, the effects of the ecdysone agonists (LD50) were investigated on the reproduction. Data showed that the three compounds affected growth of ovaries as evidenced by morphometric measurements of the ovaries from newly emerged adult females. In addition, the thickness of the chorion from basal oocytes was reduced only by RH-5992 and RH-0345. However, electron microscopic observations revealed that the three compounds had no significant effect on the fine structure of chorion. Finally, measurements of ovarian ecdysteroids' production by an enzyme immunoassay showed an increase in the hormonal amounts recorded in treated series compared to control series.