No 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.

The stable fly, Stomoxys calcitrans (Diptera: Muscidae), is a worldwide pest of livestock. Recent outbreaks of stable flies in sugarcane fields in Brazil have become a serious problem for livestock producers. Larvae and pupae found inside sugarcane stems after harvesting may indicate that stable flies use these stems as potential oviposition or larval development sites. Field observations suggest that outbreaks of stable flies are associated with the vinasse and filter cake derived from biomass distillation in sugarcane ethanol production that are used as fertilizers in sugarcane fields. Adult stable flies are attracted to vinasse, which appears to present an ideal larval development site. The primary goal of the present study is to demonstrate the role of vinasse in influencing the sensory physiological and behavioural responses of stable flies, and to identify its associated volatile attractant compounds. Both laboratory and field studies showed that vinasse is extremely attractive to adult stable flies. Chemical analyses of volatiles collected revealed a wide range of carboxylic acids, alcohols, phenols and aldehydes as potential attractant compounds. These newly identified attractants could be used to develop a tool for the attractant-baited mass trapping of stable flies in order to reduce infestations.