Behavioral and Toxicological Responses of Rhodnius prolixus (Hemiptera: Reduviidae) to the Insect Repellents DEET and IR3535.

,N-diethyl-3-methylbenzamide (DEET) is a broad-spectrum insect repellent used by millions of people since the 1950s. Ethyl 3-[acetyl(butyl)amino]propanoate (IR3535) is a repellent developed more recently that is still not used as extensively. This study compares the behavioral and toxicological effects of both substances in fifth-instar nymphs of the blood-sucking bug Rhodnius prolixus Stål (Hemiptera: Reduviidae), one of the main vectors of American trypanosomiasis (Chagas disease). Repellency was quantified using filter paper discs as experimental arenas. Half the discs were treated with solution of repellent in acetone, and the other half with acetone alone. The lowest observed effect level was identical for both substances, 74 µg/cm2. Nymph age (between 1-3 h and 99 d from last ecdysis) had no influence on repellency. Topical application of 750 µg of DEET per nymph produced a mortality rate between 0% (24 h after application) and 40% (7 d later). The same dose of IR3535 produced no mortality during the same period of time. Simultaneous treatment with piperonylbutoxide (a mixed function microsomal oxidase inhibitor) synergized the lethal effect of DEET. Only DEET increased locomotor activity in nymphs exposed to a treated surface. Nymph antennectomy abolished DEET repellency but not its effect on locomotor activity. The concentrations of both these compounds required to produce either behavioral or toxicological effects are too high to have any practical applications in the control of R. prolixus.