Lethal and behavioural effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti mosquitoes in laboratory assays

The knock‐down, mortality and ‘irritancy’ effects of three synthetic repellents (DEET, IR3535 and KBR 3023) on Aedes aegypti (L) (Diptera: Culicidae) were evaluated in the laboratory in the absence of animal bait. Filter paper tests were carried out to assess the knock‐down effect (KDt 50 and KDt 95 ) and mortality (LC 50 and LC 95 ) induced by each repellent. ‘Irritancy’ tests were carried out to compare the flight response (time to first take‐off, or FT) to increasing concentrations of repellents (2–7%) and at five distances from the treated surface (0–40 mm). DEET had an insecticidal effect (KDt 50 = 9.7 min at 7%; CL 50 = 1165 mg/m 2 ), whereas IR3535 and KBR 3023 did not. Relative to an untreated control, IR3535 was an irritant (relative irritancy or RI > 1) at doses of 5% and 7% (RI = 17.7 and 9.9, respectively), whereas DEET was an irritant at lower concentrations (RI = 12.3 at 2% DEET). KBR 3023 was the weakest irritant over the same range of concentrations (RI max = 3.6 at 6%). DEET was more of an irritant (RI 20 = 9.4) than IR3535 (RI 20 = 2.9) over a range of distances (0–20 mm), and KBR 3023 was not an irritant unless mosquitoes made contact with the treated surface. All three repellents had a significant effect on mosquitoes, but DEET exhibited a more complex mode of action than the others due to its insecticidal properties. The repellents do not behave as a single class of compounds with a common mode of action, but most probably affect different physiological systems in insects. The physiological and molecular mechanisms of repellents, especially DEET, should be investigated to ensure a better use of these molecules for skin applications and/or for treating materials against mosquitoes.