Abstract
Since the discovery in the early 1980s that 1-octen-3-ol, isolated from oxen breath, attracts tsetse fly, there has been growing interest in exploring the use of this semiochemical as a possible generic lure for trapping host-seeking mosquitoes. Intriguingly, traps baited with 1-octen-3-ol captured significantly more females of the malaria mosquito, Anopheles gambiae, and the yellow fever mosquito, Aedes aegypti, than control traps, but failed to attract the southern house mosquito, Culex quinquefasciatus. Additionally, it has been demonstrated that this attractant is detected with enantioselective odorant receptors (ORs) expressed only in maxillary palps. On the basis of indoor behavioral assays it has even been suggested that 1-octen-3-ol might be a repellent to the southern house mosquito. Our approach was two-prong, i.e., to isolate 1-octen-3-ol-sensitive ORs expressed in maxillary palps and antennae of southern house female mosquito, and test the hypothesis that this semiochemical is a repellent. An OR with high transcript levels in maxillary palps, CquiOR118b, showed remarkable selectivity towards ( R)-1-octen-3-ol, whereas an OR expressed in antennae, CquiOR114b, showed higher preference for ( S)-1-octen-3-ol than its antipode. Repellency by a surface landing and feeding assay showed that not only racemic, but enantiopure ( R)- and ( S)-1-octen-3-ol are repellents at 1% dose thus suggesting the occurrence of other ( S)-1-octen-3-ol-sensitive OR(s). Female mosquitoes with ablated maxillary palps were repelled by 1-octen-3-ol, which implies that in addition to OR(s) in the maxillary palps, antennal OR(s) are essential for repellency activity.
Highlights
Since the discovery in the early 1980s that 1-octen-3-ol, isolated from oxen breath, attracts tsetse fly, there has been growing interest in exploring the use of this semiochemical as a possible generic lure for trapping host-seeking mosquitoes
Odorant receptors housed in the maxillary palps of the malaria mosquito[6] and yellow fever mosquito[9], AgamOR8 and AaegOR8, respectively, showed significant preference for the (R)-enantiomer when co-expressed in Xenopus oocytes along with the obligatory co-receptor Orco
Dataset 1: Quantitative RT-PCR (qPCR) data obtained for CquiOR114b, CquiOR118b, and CquiOrco with cDNAs from antennae and maxillary palps
Summary
Since the discovery in the early 1980s that 1-octen-3-ol, isolated from oxen breath, attracts tsetse fly, there has been growing interest in exploring the use of this semiochemical as a possible generic lure for trapping host-seeking mosquitoes. In-door behavioral studies demonstrated that at two doses (R)-(-) 1-octen-3-ol caused an increase in activation for Cx. quinquefasciatus, and at seven of the doses tested (R:S)-1-octen-3-ol mixture (84:16) caused significantly more mosquitoes to sustain their flight and reach the capture chambers in a two-choice, Y-tube olfactometer suggesting that the isomeric mixture has an excitatory effect[7]. They observed that at the highest concentration, mosquitoes that reached the capture chambers moved towards the control chamber rather than the arm containing (R)-(-)-1-octen-3-ol per se or in mixtures, i.e., a reduced attraction response mediated by the (R)-enantiomer[7]. These findings provide evidence that peripheral reception of 1-octen-3-ol is enantioselective at the maxillary palps, but random (racemic) at the antennae
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