Decrease in DEET repellency caused by nitric oxide in Rhodnius prolixus

Abstract

N,N-diethyl-3-methylbenzamide (DEET) is widely used as an insect repellent; however, little is known about its mode of action. On the other hand, nitric oxide (NO) participates in the olfaction transduction pathway of insects. In this work, nitroso-acetyl-cysteine (SNAC), a nitric oxide donor, or dibutyril-cyclic-GMP (db-cGMP), the cyclic nucleotide analog, were applied on fifth instar nymphs of Rhodnius prolixus before exposing them to DEET, to obtain information about the possible role of NO/cGMP system in the olfaction process. In the first place, we exposed the nymphs to several DEET concentrations (70, 700, 1,750, and 3,500 microg/cm2). All these concentrations produced a repellent effect. A decrease in repellency during the course of the experiment was observed when the nymphs were exposed to high concentrations of DEET (700 and 1,750 microg/cm2), suggesting an adaptation phenomenon. The pre-treatment of the insects with 15 microg /insect of SNAC or 2 microg/insect of db-cGMP produced a reduction of the repellency. An increase in locomotor activity was observed in insects exposed to 350 or 700 microg/cm2 DEET. Although exposure to 70 microg/cm2 DEET produced a high repellency response, it did not modify the insects' locomotor activity. Insects treated with two doses of SNAC before being exposed to 350 microg/cm2 of DEET showed no differences in locomotor activity compared to controls.

Deterrence of feeding in Rhodnius prolixus (Hemiptera: Reduviidae) after treatment of antennae with a nitric oxide donor

“…The decrease in the response to the DEET repellent (Sfara et al, 2008) and the reluctance to feed as well as the decrease in the response to CO2 of insects treated with SNAC reported here, are consistent with previous studies that suggest that the NO/cGMP is the signalling system of the olfactory adaptation process.…”

“…In a previous study, we demonstrate that the behavioural response of R. prolixus to DEET decreases after prolonged exposure to this repellent, suggesting a possible adaptation phenomenon (Sfara et al, 2008). We also observed a decrease in the response to DEET after treating R. prolixus antennae with the NO donor SNAC or db-cGMP, which might indicate that the NO/cGMP pathway is involved in adaptation.…”

“…Two concentrations of this compound were applied: 1 or 2 µg/insect. These concentrations were chosen based on a previous study in our laboratory, which indicates a dosedependent decrease in the behavioural response to DEET when topically applied to the antennae of fifth instar nymphs of R. prolixus (Sfara et al, 2008).…”

“…However, the insect's behavioural response was only studied in a few cases, mainly in the locust (Newland & Yates, 2007;Wenzel et al, 2005). In a previous study, we show that treating R. prolixus nymphs with the NO donor S-nitroso-N-acetylcysteine (SNAC) produces a decrease in the behavioural response to the classical insect repellent N,N-diethyl-3-methylbenzamide (DEET) (Sfara et al, 2008). A similar result is obtained when the antennae of nymphs are treated with the cGMP analog dibutiryl-cyclic-guanosine-monophosphate (dbcGMP).…”

Rhodnius prolixus smells repellents: Behavioural evidence and test of present and potential compounds inducing repellency in Chagas disease vectors

“…Concerning triatomine vectors of Chagas disease, different aspects of their response to DEET have been analysed in detail, as for example the spatial distribution and olfactory orientation of Triatoma infestans (Alzogaray et al, 2000), the effect of nitric oxide on repellency induced by DEET in Rhodnius prolixus (Sfara et al, 2008) and the loss of sensitivity to DEET following preexposition in the same species (Sfara et al, 2011). Some other relevant aspects, such as the exact way in which it modulates the behaviour of bugs or its relative efficacy as compared to other compounds, remain however unknown.…”