<scp>L</scp>‐lactic acid: a human‐signifying host cue for the anthropophilic mosquito <i>Anopheles gambiae</i>

Dekker, Teun; Steib, B.; Cardé, Ring T.; Geier, Martin

doi:10.1046/j.0269-283x.2002.00345.x

Cited by 152 publications

(149 citation statements)

References 33 publications

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“…The low sensitivity of the lactic acid-detecting ORNs and the low vapor phase of lactic acid required large amounts of stimulus (10 g) thus defeating the purpose of comparing neuronal activity in the presence and absence of DEET. We also tested the yellow fever mosquito, Aedes aegypti, but preliminary recordings (data not shown) showed a similar low sensitivity of the peg sensilla to lactic acid, in line with both the high titer of lactic acid in human sweat (8) and the doses required for mosquito attraction (9). Given the technical difficulty of reexamining DEET effect on lactic acid detection and considering DEET repellency to mosquitoes attracted only to carbon dioxide (4, 7) we then examined the possible effect of DEET on CO 2 detection.…”

Section: Resultsmentioning

confidence: 99%

Mosquitoes smell and avoid the insect repellent DEET

Syed

Leal

2008

Proc. Natl. Acad. Sci. U.S.A.

287

231

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The insect repellent DEET is effective against a variety of medically important pests, but its mode of action still draws considerable debate. The widely accepted hypothesis that DEET interferes with the detection of lactic acid has been challenged by demonstrated DEETinduced repellency in the absence of lactic acid. The most recent hypothesis suggests that DEET masks or jams the olfactory system by attenuating electrophysiological responses to 1-octen-3-ol. Our research shows that mosquitoes smell DEET directly and avoid it. We performed single-unit recordings from all functional ORNs on the antenna and maxillary palps of Culex quinquefasciatus and found an ORN in a short trichoid sensillum responding to DEET in a dosedependent manner. The same ORN responded with higher sensitivity to terpenoid compounds. SPME and GC analysis showed that odorants were trapped in conventional stimulus cartridges upon addition of a DEET-impregnated filter paper strip thus leading to the observed reduced electrophysiological responses, as reported elsewhere. With a new stimulus delivery method releasing equal amounts of 1-octen-3-ol alone or in combination with DEET we found no difference in neuronal responses. When applied to human skin, DEET altered the chemical profile of emanations by a ''fixative'' effect that may also contribute to repellency. However, the main mode of action is the direct detection of DEET as indicated by the evidence that mosquitoes are endowed with DEET-detecting ORNs and corroborated by behavioral bioassays. In a sugar-feeding assay, both female and male mosquitoes avoided DEET. In addition, mosquitoes responding only to physical stimuli avoided DEET.DEET mode of action ͉ DEET-detecting neuron ͉ fixative effect of DEET ͉ mosquito olfaction ͉ surface-landing bioassay T he insect repellent DEET, N,N-diethyl-3-methylbenzamide, has been used for Ͼ50 years, with 200 million people using it worldwide to reduce their risk of vector-borne diseases (1) but its mode of action has yet to be elucidated. The report that DEET modulates the physiological response of lactic acid-sensitive olfactory receptor neurons (ORNs) in the antennae of the yellow fever mosquito, Aedes aegypti (2), led to the hypothesis that DEET may interfere with and inhibit the response of the olfactory system to a normally attractive chemical signal (3). This notion of ''jamming'' the olfactory system has been substantiated, on the one hand, by behavioral observations indicating that lactic acid per se is a mosquito attractant and suggesting that DEET inhibits attraction to lactic acid (4, 5) and by the recent report on DEET attenuation of mosquito response to 1-octen-3-ol (6). However, repellency solely by inhibition of lactic acid detection was challenged by indoor (4) and field experiments (7) demonstrating the repellent effect of DEET with carbon dioxide as the only attractant. Intrigued by this controversy and puzzled by the dichotomy between sensory physiology and behavioral observations, we undertook a multidisciplinary approach aimed at ...

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Section: Resultsmentioning

confidence: 99%

Mosquitoes smell and avoid the insect repellent DEET

Syed

Leal

2008

Proc. Natl. Acad. Sci. U.S.A.

287

231

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“…In contrast, S1 sensillum neurons showed no response to isovaleric acid, which evokes strong ELG responses ( Fig. 1) as well as 1-octen-3-ol, 2-methyl phenol, 4-methyl phenol, indole, geranyl acetone, and ammonia, which have been identified as human sweat compounds and shown to elicit significant responses from A. gambiae antennal preparations (14,15,(19)(20)(21), (Fig. 1D).…”

Section: Characterization Of Olfactory Responses From the Proboscis Omentioning

confidence: 99%

Olfactory responses in a gustatory organ of the malaria vector mosquito Anopheles gambiae

Kwon

Lu²,

Rützler³

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

138

149

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The proboscis is an important head appendage in insects that has primarily been thought to process gustatory information during food intake. Indeed, in Drosophila and other insects in which they have been identified, most gustatory receptors are expressed in proboscis neurons. Our previous characterization of the expression of AgOR7, a highly conserved odorant receptor (OR) of the Afrotropical malaria vector mosquito Anopheles gambiae in the labellum at the tip of the proboscis was suggestive of a potential olfactory function in this mosquito appendage. To test this hypothesis, we used electrophysiological recording and neuronal tracing, and carried out a molecular characterization of candidate OR expression in the labellum of A. gambiae. These studies have uncovered a set of labial olfactory responses to a small spectrum of human-related odorants, such as isovaleric acid, butylamine, and several ketones and oxocarboxylic acids. Molecular analyses indicated that at least 24 conventional OR genes are expressed throughout the proboscis. Furthermore, to more fully examine AgOR expression within this tissue, we characterized the AgOR profile within a single labial olfactory sensillum. This study provides compelling data to support the hypothesis that a cryptic set of olfactory neurons that respond to a small set of odorants are present in the mouth parts of hematophagous mosquitoes. This result is consistent with an important role for the labellum in the close-range discrimination of bloodmeal hosts that directly impacts the ability of A. gambiae to transmit malaria and other diseases.olfaction ͉ proboscis ͉ insect ͉ olfactory receptor neuron

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“…Female Anopheles gambiae, the main malarial vector in Sub-Saharan Africa, rely on their sense of smell for host seeking, oviposition and sugar feeding, whereas males respond mostly to plant odors (Foster, 1995;Takken and Knols, 1999). Many field and laboratory studies have shown that female A. gambiae respond to odors emitted from humans to find a blood meal, and wind tunnel experiments and electroantennograms (EAG) have identified a variety of singlechemical compounds in human sweat that stimulate olfactory neurons and attract female mosquitoes (Cork and Park, 1996;Costantini et al, 2001;Dekker et al, 2002;Meijerink et al, 2001;Meijerink and van Loon, 1999;Qiu et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Sex-biased expression of odorant receptors in antennae and palps of the African malaria vector Anopheles gambiae

Iatrou

Biessmann

2008

Insect Biochemistry and Molecular Biology

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At the heart of the odor recognition process in all animals are G-protein-coupled receptors, which are seven-transmembrane domain proteins that initiate G-protein-mediated signaling cascades when activated by their ligands. Odorant receptors (ORs) are a large, diverse family of proteins with some 80 members in the mosquito Anopheles gambiae. With the assumption that more sensilla on female antennae are tuned to human odors than on male antennae, comparison of specific OR mRNA levels in male and female antennae can provide an indication as to which receptors may be stimulated by host odors. We have used RT PCR and quantitative real-time PCR (qRT PCR) to investigate sexbiased expression levels of 80 A. gambiae ORs in male and female antennae and maxillary palps. On the basis of prevalence of expression in female antennae and on a strong female relative to male expression bias we identified a short list of ORs that are likely involved in host odor recognition by female mosquitoes.

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L‐lactic acid: a human‐signifying host cue for the anthropophilic mosquito Anopheles gambiae

Cited by 152 publications

References 33 publications

Mosquitoes smell and avoid the insect repellent DEET

Mosquitoes smell and avoid the insect repellent DEET

Olfactory responses in a gustatory organ of the malaria vector mosquito Anopheles gambiae

Sex-biased expression of odorant receptors in antennae and palps of the African malaria vector Anopheles gambiae

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