Host plant forensics and olfactory-based detection in Afro-tropical mosquito disease vectors

The global spread of vector-borne diseases remains a worrying public health threat, raising the need for development of new combat strategies for vector control. Knowledge of vector ecology can be exploited in this regard, including plant feeding; a critical resource that mosquitoes of both sexes rely on for survival and other metabolic processes. However, the identity of plant species mosquitoes feed on in nature remains largely unknown. By testing the hypothesis about selectivity in plant feeding, we employed a DNA-based approach targeting trnH-psbA and matK genes and identified host plants of field-collected Afro-tropical mosquito vectors of dengue, Rift Valley fever and malaria being among the most important mosquito- borne diseases in East Africa. These included three plant species for Aedes aegypti (dengue), two for both Aedes mcintoshi and Aedes ochraceus (Rift Valley fever) and five for Anopheles gambiae (malaria). Since plant feeding is mediated by olfactory cues, we further sought to identify specific odor signatures that may modulate host plant location. Using coupled gas chromatography (GC)-electroantennographic detection, GC/mass spectrometry and electroantennogram analyses, we identified a total of 21 antennally-active components variably detected by Ae. aegypti, Ae. mcintoshi and An. gambiae from their respective host plants. Whereas Ae. aegypti predominantly detected benzenoids, Ae. mcintoshi detected mainly aldehydes while An. gambiae detected sesquiterpenes and alkenes. Interestingly, the monoterpenes β-myrcene and (E)-β-ocimene were consistently detected by all the mosquito species and present in all the identified host plants, suggesting that they may serve as signature cues in plant location. This study highlights the utility of molecular approaches in identifying specific vector-plant associations, which can be exploited in maximizing control strategies such as such as attractive toxic sugar bait and odor-bait technology.S1 Table. List of compounds identified from five host plants of Afro-tropical mosquito species and relative amounts ± SEM (ng). The compounds were identified from headspace volatiles of LN = Lenonotis nepetifolia, RC = Ricinus communis, SA = Senna alata (host plants of Anopheles gambiae), PD = Pithecellobium dulce (host plant of Aedes aegypti) and OFI = Opuntia ficus-indica (host plant of Aedes mcintoshi and Aedes ochraceus).S1 Fig. Mass spectra and chemical structures of electrophysiologically active compounds which were confirmed with synthetic standards. A) hexanal, B) (E)-2-hexenol, C) β-myrcene, D) (E)-β-ocimene, E) (Z)-linalool oxide (furanoid), F) (Z)-linalool oxide (pyranoid), G) indole, and H) benzaldehyde.Swedish International Development Cooperation Agency (Sida) studentship to VON. Partial funding was also received from the UK's Department for International Development (DFID), the Swiss Agency for Development and Cooperation (SDC), and the Kenyan Government.http://www.plosntds.orgam2019Zoology and Entomolog