Changes in the repellent behavior of Rhodnius prolixus after continuous exposure to DEET

V. SFARA, G. A. MOUGABURE CUETO, E. N. ZERBA Y R. A. ALZOGARAY.

Colonia del Sacramento

Congreso; 1st Latin American Meeting of Chemical Ecology; 2010

Asociación Latinoamericana de Ecología Química

N, N-diethyl-m-methylbenzamide (DEET) is the active ingredient of most insect repellents. Its efficacy has been proved in a number of insect species [1], however very few is known about its mode of action. In this work we study changes in the repellency of fifth instar nymphs of Rhodnius prolixus to DEET, after being continuously exposed to high concentrations of this repellent. A circular filter paper treated with a solution of DEET in acetone (2 mg/cm2) [2] was placed in a closed plastic container, where a nymph of R. prolixus was allowed to walk on the treated surface. Then, the repellency to DEET of each individual was tested in a circular arena divided into halves: one half was treated with DEET and the other one with acetone. Repellency was expressed as Repellency Coefficients (RC). Three variables were considered: the time of continuous exposure (1, 5, 10 or 20 minutes), the time after exposure (10, 20 and 30 min), and the test concentration of DEET. When the test concentration of DEET was lower than the exposure concentration, a decrease in the RCs was observed in insects exposed 5, 10 or 20 minutes compared with control groups (without continuous exposure to DEET); 1 minute exposure did not decrease the RC. The response to DEET was recovered 10 minutes after treatment in insects exposed 5 or 10 minutes; and 20 minutes after treatment when insect were exposed 20 minutes. No decrease in the RCs was observed when repellency was tested with a concentration of DEET higher than the concentration used in the treatments. The decrease of the repellency after continuous exposure of R. prolixus nymphs to the repellent and the fast recovery of the response suggest a sensory adaptation phenomenon. We propose a role of the sensory system, probably olfactory, in the detection of DEET.