Studies on sand fly resting habitats, plant feeding patterns and volatilome in a leishmaniasis endemic area of Kenya

Abstract

Phlebotomine sand flies (Diptera: Psychodidae) are vectors of the Leishmania parasites causing leishmaniasis which has public health importance worldwide. Improved understanding of the sand fly ecology can open avenues to developing new control measures. Plant feeding and habitat selection are understudied aspects of the ecology of sand flies especially Afrotropical species, whose interaction can affect their distribution and vectorial capacity. Chapter one is a general introduction to this study. Chapter two addresses whether adult sand fly distribution varies in different habitats used as resting/breeding sites, as well as explores the underlying volatile chemistry. Sand flies were trapped using CDC light traps in three selected habitats: houses indoors, animal shelters, and termite mounds, through cross-sectional surveys from a leishmaniasis endemic area of Baringo County, Kenya. Sand fly abundance and diversity varied between the habitats; being most abundant and diverse in animal shelters followed by termite mound and houses indoors. Gas chromatography-mass spectrometry (GC-MS) analysis of volatiles from the habitat associated substrates viz: human foot odour (house indoors); cow dung (animal shelters) and termite vent (termite mound), revealed variation in volatile organic compound (VOC) profiles yet with commonalities across the habitats including 1-octen-3-ol, 6-methyl-5-hepten-2-one, m-cresol, and p-cresol, with implicated in the sensory ecology of sand flies and other arthropods. In chapter three, the sand fly plant feeding habits and underlying volatile chemistry was assessed. The cold-anthrone test for evidence of recent plant feeding showed that fructose positivity rates did not differ between both sexes of Phlebotomus and Sergentomyia species and those sampled from indoor and outdoor habitats. Plant DNA amplification and sequencing of the rbcL gene in the gut of fructose-positive specimen implicated mainly Acacia species (Vachellia tortilis, Senegalia laeta, Vachellia nilotica, and Faidherbia albida) in the family Fabaceae as host plants for P. martini (visceral leishmaniasis vector), P. duboscqi (cutaneous leishmaniasis vector), and Sergentomyia species. Nutritional profiling via HPLC of the gut of wild sand flies and leaves of the identified Acacia plants found fructose as commonly detected sugar in both sources. Further, GC-MS and analysis of similarities (ANOSIM) of the headspace volatile profiles identified benzyl alcohol, (Z)-linalool oxide, (E)-β-ocimene, p-cymene, p-cresol, and m-cresol, as discriminating compounds between the plant volatiles. In Chapter four the behavioural responses of P. duboscqi in the laboratory to linalool oxide, ocimene, p-cymene, p-cresol, and m-cresol, singly and in blends are described. In dose-response assays, each compound, increased the responses of males and females over controls, but their optimum attractive doses varied between the sexes. Two five-component blends (one for males and another for females) based on the optimal attractive doses, significantly attracted each sex to varying levels compared to 1-octen-3-ol (positive control), a known sand fly attractant. In pairwise assays, only males were attracted to both blends at varying levels. Overall, fructose may play a significant role in the energetics of examined sand flies. VOCs may contribute to the structure of sand flies in associated habitats and identified plant-derived attractants can potentially be exploited as lures to improve Afrotropical sand fly surveillance and control.