Lutzomyia longipalpis (Lutz & Neiva) is the vector of Leishmania infantum (Nicolle), the aetiological agent of visceral leishmaniasis in the New World. It has been shown by several authors that Lu. longipalpis represents a complex of at least three species. Adults of this species are known to mediate mating and oviposition using pheromones. This study aimed to investigate an aspect of their behaviour that had previously been neglected, namely the responses of female Lu. longipalpis to human kairomones. It was found that females could be lured by volatiles extracted from skin secretions. Pentane and ether extracts were equally effective in attracting female Lu. longipalpis. Whole pentane extracts were further fractionated by column chromatography into a polar fraction (ether-soluble) and a non-polar fraction (pentane-soluble). Testing both fractions for sandfly activity showed that only the pentane-soluble fraction was attractive to Lu. longipalpis. Host odours not only appeared to explain the variation in attraction of human volunteers, but were also found to be potentially responsible for sandfly biting distributions on a host. Female sandflies exhibited a marked biting preference for the ears of a human volunteer. Cross-mating experiments with putative members of the Lu. longipalpis complex, Jacobina (3-methyl-a-himachelene) and Marajo (Cembrene-producing pheromone type), provided direct evidence of prezygotic isolation between the two studied populations (i. e. by examining insemination rates and pheromone production in FI males). This result explains why two coexisting pheromone types are never detected in single male sandfiies collected in the wild. The cross-mating experiments additionally found partial post-zygotic barriers, with significantly reduced eggs production and egg hatching rates in F1 progeny. A series of independent bioassays provided evidence for innate differences in anthropophily between at least two allopatric populations of Lu. longipalpis. The main behavioural differences detected were in (1) the mean time to bite on a human host during a biting selection trial, (2) the behavioural response to ear washing extracts (landings on impregnated filter papers), and (3) the SAQ (Sandfly Activity Quotient) response (landings) to volatlles deposited onto handled glass Petri dishes (for the two most contrasting sandfly populations: Jacobina and Marajo). Finally, preliminary wind-tunnel studies undertaken with golden hamsters infected with Leishmania infantum suggested a change in the overall body odour composition of the host, making it more attractive to female Lu. longipalpis. Gas chromatography analysis of entrained volatile odours from infected and non-infected hamsters showed a large number of peaks in chromatograms from both animals. A total of 10 extra compounds, eluted from 10 to 16 minutes of retention time, were present in samples from infected hamsters, but were absent in those obtained from non-infected hamsters.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:344056 |
| Date | January 2000 |
| Creators | Rebollar-Tellez, Eduardo Alfonso |
| Publisher | Keele University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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