Effects of ecdysone agonist halofenozide against Culex pipiens

Halofenozide is a novel insect growth regulator belonging to the class of non-steroidal ecdysone agonists that are developed as insecticides particularly against Lepidoptera. In this study, halofenozide (23% EC) was evaluated against newly molted fourth-instar larvae of the house mosquito, Culex pipiens (Diptera: Culicidae), that were exposed for 24 h under standard laboratory conditions according to World Health Organization recommendations. Typically, halofenozide affected C. pipiens molting with an LC 50 of 12.58 μg/L; intoxicated specimens failed to ecdyse and died trapped into their exuvium. To better understand the physiology of action of halofenozide, enzyme immunoassay measurements with whole larval bodies indicated that the ecdysteroid titers were affected by halofenozide, and the thickness of both the old and newly secreted cuticle was increased in treatments as was seen after histological analysis.