Annual Research & Review in Biology

Aims: Insect growth regulators (IGRs) offer alternatives to conventional chemical larvicides that pose problem of resistance and environmental safety. However, only a limited number of IGRs have been approved for use in mosquito control. The present investigation was to evaluate the insecticidal activity of a non-steroidal ecdysteroid agonist, methoxyfenozide (RH-2485), against last-instar larvae of Culiseta morsitans (Culicidae: Diptera) under the laboratory conditions, and its effect on fecundity and fertility of females.
Methodology: Based on preliminary bioassays, five concentrations ranging from 0.012 to 0.072mg/L were tested. The larvicidal test was made according to the World Health Organization (WHO) protocol standard by exposing newly ecdysed fourth- instar larvae for 24h. CL₅₀ value of methoxyfenozide value was determined by probit analysis.
Results: The insecticidal activity of methoxyfenozide result in a dose- dependent reduction in adult emergence. In addition, larval mortality was relatively important compared with the mortality recorded for the other following developmental stages. The larval mortality varies between 16.84±3.89 % and 66.24±3.50% for 0.012 mg/L and 0.072 mg/L, respectively, and LC₅₀ value was 0.059mg/L. The ecdysteroidal activity of this compound caused premature induction of larval moulting and incomplete pupation. Also, the different types of morphogenetic aberrations in the larva, pupa and adult after exposure to methoxyfenozide are illustrated (larval-pupal and pupal-adult). Moreover, the tested compound greatly affected the reproductive parameters of surviving females derived from larval treatment. Methoxyfenozide caused a significant reduction of fecundity and fertility (P<0,001). Also, no egg laying has been recorded with the higher concentration 0.072 mg/L, which produced 100% of sterility.
Conclusion: Methoxyfenozide is an efficient insect growth regulator for controlling mosquito populations. This compound may prove to be an effective larvicide for treatment of mosquito, to decrease the frequency of pathogen transmission to humans and animals.