Fermenting molasses and a synthetic odour blend to attract blood-fed Anopheles coluzzii

Collecting blood-fed mosquitoes to monitor pathogen presence or to gather information on the host blood meal is often challenging. Fermenting molasses can be used to produce carbon dioxide to attract host-seeking mosquitoes, however, earlier work indicated that it may also attract blood-fed mosquitoes in the field. In the current study, these field results were validated in an experimental setting using a large cage setup with Anopheles coluzzii (Diptera, Culicidae). Blood-fed mosquitoes were indeed attracted to fermenting molasses with the highest attraction at 72 hours post feeding, which was used for subsequent experiments. Next, it was tested if fermentation of molasses is required for attraction, and whether it acts as an oviposition attractant, increases egg laying, or increases mosquito survival. The compounds that could be responsible for attraction were identified by combined electrophysiology and chemical analyses and formulated into a synthetic blend. Fermenting molasses attracted blood-fed mosquitoes in the large cage study, while fermenting sugar and non-fermenting molasses did not. The fecundity of blood-fed mosquitoes increased after feeding on fermenting molasses, however, compounds emanating from molasses did not trigger oviposition. The synthetic blend attracted blood-fed mosquitoes and may be used to determine mosquito host selection and for xenomonitoring, as 'flying syringes' to detect non-vector borne pathogens.