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.

Keywords: Leishmania; Lutzomyia longipalpis; disease prevention; host choice; sex-aggregation pheromone; vector biology.

Figure 1

(a) Conceptual representation of host choice model: the behaviour of a sand fly depends on the distance and the strength of stimulus received from various sources: hosts (humans, dogs and chickens) and synthetic pheromone traps. (b) Location of households [30].

Figure 2

Proportions of Lu. longipalpis as a function of: (a) amount of pheromone (for the experiment A); (b) number of chickens (for the experiment C); (c) amount of pheromone and number of chickens (simulation results). Measured mean and standard deviation are shown in blue and fitted curves in black in (a) and (b).

Figure 3

Lu. longipalpis estimated preference for hosts and pheromones: (a) in the absence of the synthetic pheromone; (b) in the presence of the synthetic pheromone.