Modelling Sand Fly Lutzomyia longipalpis Attraction to Host Odour: Synthetic Sex-Aggregation Pheromone Dominates the Response

Abstract

Zoontic visceral leishmaniasis (ZVL) due to Leishmania infantum is a potentially fatal protozoan parasitic disease of humans and dogs. In the Americas, dogs are the reservoir and the sand fly, Lutzomyia longipalpis, the principal vector. A synthetic version of the male sand fly produced sex-aggregation pheromone attracts both female and male conspecifics to co-located insecticide, reducing both reservoir infection and vector abundance. However the effect of the synthetic pheromone on the vector’s “choice“ of host (human, animal reservoir, or dead-end host) for blood feeding in the presence of the pheromone is less well understood. In this study, we developed a modelling framework to allow us to predict the relative attractiveness of the synthetic pheromone and potential alterations in host choice. Our analysis indicates that the synthetic pheromone can attract 53% (95% CIs: 39%–86%) of host-seeking female Lu. longipalpis and thus it out-competes competing host odours. Importantly, the results suggest that the synthetic pheromone can lure vectors away from humans and dogs, such that when co-located with insecticide, it provides protection against transmission leading to human and canine ZVL.

Chapter 13: Sand fly sex/aggregation pheromones

“…Only in Lu. longipalpis s.l., the Latin American vector of Leishmania infantum, has one of the sex/aggregation pheromones of the species complex been identified, characterised, synthesised and demonstrated to have potential as a vector control tool (Courtenay et al, 2019;Hamilton, 2008;Retkute et al, 2021). Much work, however, remains to be done to understand the integration of the sex/aggregation pheromones within other odour based communication channels, including those relating to host finding (Ortiz et al, 2020;Rebollar-Tellez et al, 1999) and oviposition site location Kowacich et al, 2020) as well as within visual (Mellor and Hamilton, 2003;Mellor et al, 1996) and acoustic ecology (Vigoder et al, 2020).…”

“…The synthetic pheromone, thus, out-competes alternative attractive odours from humans and dogs, thereby reducing risk of Le. infantum transmission (Retkute et al, 2021).…”

Insecticide-impregnated netting: A surface treatment for killing Lutzomyia longipalpis (Diptera: Psychodidae), the vector of Leishmania infantum

“…However, doubling or quadrupling the area of insecticide-impregnated netting might bring additional relative benefits without the need to treat the whole surface area. Overall, the approach is potentially cost-effective, if the longevity of the treatment is assured, as it is simple to apply and can be combined with synthetic sex/aggregation pheromone to provide a readily accessible intervention measure for leishmaniasis control ( Courtenay et al., 2019 ; Retkute et al., 2021 ).…”

“…longipalpis form aggregations on or near host animals for mating and female blood-feeding with chicken sheds being a common aggregation site in peridomestic environments ( Kelly and Dye, 1997 ). Although it is not clear why some aggregation sites are favoured over others, aggregation behaviour is largely driven by the male produced sex-aggregation pheromone ( Spiegel et al., 2016 ; Bell et al., 2018 ; Retkute et al., 2021 ). The use of insecticide has a disruptive effect on Lu.…”

“…A trial of the synthetic sex-aggregation pheromone, ( ± )-9-methylgermacrene-B ( Krishnakumari et al., 2004 ), formulated in a long-lasting controlled release device ( Bray et al., 2009 , 2014 ) co-located with sprayed microencapsulated λ-cyhalothrin (Demand CSW; BASF PLC, Cheshire, UK) in chicken roosting sites significantly reduced Lu. longipalpis densities, canine Leishmania parasite infection incidence, tissue loads and canine seroconversion incidence and established the potential for this strategy to reduce disease incidence ( Courtenay et al., 2019 ; Gonçalves et al., 2021 ; Retkute et al., 2021 ).…”