Geosmin attractsAedes aegyptimosquitoes to oviposition sites

Abstract

Geosmin is one of the most recognizable and common microbial smells on the planet. Some insects, like mosquitoes, require microbial-rich environments for their progeny, whereas for other insects such microbes may prove dangerous. In the vinegar fly Drosophila melanogaster, geosmin is decoded in a remarkably precise fashion and induces aversion, presumably signaling the presence of harmful microbes. We have here investigated the effect of geosmin on the behavior of the yellow fever mosquito Aedes aegypti. In contrast to flies, geosmin is not aversive in mosquitoes but stimulates egg-laying site selection. Female mosquitoes could associate geosmin with microbes, including cyanobacteria consumed by larvae, who also find geosmin -as well as geosmin producing cyanobacteria -attractive. Using in vivo multiphoton imaging from mosquitoes with pan-neural expression of the calcium reporter GCaMP6s, we show that Ae. aegypti code geosmin in a similar fashion to flies, i.e. with extreme sensitivity and with a high degree of selectivity. We further demonstrate that geosmin can be used as bait under field conditions, and finally we show that geosmin, which is both expensive and difficult to obtain, can be substituted by beetroot peel extract, providing a cheap and viable mean of mosquito control and surveillance in developing countries.

Progress in the use of genetic methods to study insect behavior outside Drosophila

“…Thus, oviposition sites need to be carefully selected by the females. Two recent studies have found that Aedes aegypti mosquitoes prefer to lay their eggs in geosmin-scented water [65], and tend to avoid salty water [66]. Neurons that respond to salt and water were found in the mosquitoes' legs, and geosmin-sensing neurons -in the antennae.…”

“…Further implementation of genetic methods, e.g. live imaging of neuronal responses as done in mosquitoes [65,66], could help us understand the gene-specific representation of sensory cues in an insect's brain.…”

“…First steps in this direction have been taken in Anopheles gambiae [83,84] and Aedes aegypti [85] by employing the fluorescent calcium indicator GCaMP to image live neuronal responses from the peripheral organs and the brain of mosquitoes. The same approach has been taken to study Aedes oviposition choices [65,66].…”

“…By using live Ca 2+ imaging of genetically encoded activity indicators, we can now investigate the neuronal basis of the observed behavioral phenotypes. This method has been elegantly used to study oviposition choices in Aedes aegypti [65,66] (Fig 2D). Gravid mosquito females lay their eggs in or near water sources, because their larvae and pupae are aquatic.…”

“…Live Ca 2+ imaging of ventral nerve cord that is innervated by ppk301 expressing neurons from the mosquito legs, has shown that these neurons responds both to water and to NaCl, implying that there must be a parallel neuronal pathway that prevents oviposition in salty water in wild-type Aedes. Live Ca 2+ imaging from the Aedes antennal lobe has been used to observe sparse neuronal responses to geosmin, an oviposition attractant [65]. The preference for geosmin has been abolished in ORCO mutant mosquitoes, indicating that, as in Drosophila, geosmin binds an ORCO-dependent receptor.…”