Nectar feeding and volatile chemical signatures influencing host plant selection in major Afrotropical mosquito disease vectors

Abstract

Although it is widely accepted that plant resources play an important role in the biology of mosquito species, the preferred mosquito host plants in the natural habitats remain largely unknown. The persistence of mosquito-borne diseases and the re-emergence of others such as Zika have created the need for novel control strategies with plant feeding becoming a new focus for such strategies. Effective deployment of these new tools requires an accurate identification of preferred host plant species that are attractive to mosquitoes. Chapter two of this study explored the potential of a single component plant-based lure, linalool oxide (LO), previously developed for malaria vectors in trapping other mosquito species important in the transmission of Rift Valley fever (RVF) and dengue diseases. LO performed as well as human-based BioGent (BG) lure and animal-based HONAD in trapping female RVF vectors, Aedes mcintoshi and Ae. ochraceus when combined with CO2 but performed poorly in the absence of carbon dioxide. On the other hand, LO was as good as BG lure in trapping female Ae. aegypti and was better than the BG lure in trapping males of this species both in the presence and absence of CO2. To improve on the performance of this single-component blend, chapter three sought to identify the natural plant species utilised by malaria vectors Anopheles gambiae s.l., dengue vectors Aedes aegypti and Rift Valley fever vector Ae. mcintoshi and Ae. ochraceus. Three plant-specific gene targets were used to amplify and identify the preferred plant DNA from the mid-guts of these species. A total of three plant species were identified as host plants for malaria vectors, one for dengue vectors and two for RVF vectors. These host plants were further evaluated for their nutritional value using first generation field collected Ae. aegypti as a model through a series of survival, fecundity and egg hatchability assays as well as chemical analyses. Differential survival rates of Ae. aegypti on the five plants was observed, partly explained by qualitative and vi quantitative differences in sugar reward from the plants. Differences in oviposition rates and egg hatchability were also observed which was in tandem with amino acid reward obtained from these sources. In chapter four, the study sought to develop a potent plant-based lure by exploiting chemical cues utilised by different Afrotropical mosquito species to locate their preferred natural host plants. The study revealed a clear difference in the classes of volatile organic compounds that dominate the fragrance of different host plants. Electrophysiological assays revealed chemical convergence in detection of hexanal, hexenol isomers, ocimene, linalool oxide and decanal for both Ae. Aegypti and Anopheles gambiae s.l. A three-component lure was developed and field evaluated against Ae. aegypti. This lure showed a superior performance to both linalool oxide and commercial BG lure in trapping male and female Ae. aegypti. Together, these findings indicate the potential of exploiting plant feeding targeted strategies in the management of Afrotropical mosquito species.