Susceptibility of wild-caught Lutzomyia longipalpis (Diptera: Psychodidae) sand flies to insecticide after an extended period of exposure in western São Paulo, Brazil

Abstract

BackgroundIn Brazil, members of the sand fly species complex Lutzomyia longipalpis transmit Leishmania infantum, a protist parasite that causes visceral leishmaniasis. Male Lu. longipalpis produce a sex pheromone that is attractive to both females and males. During a cluster randomised trial, to determine the combined effect of synthetic sex-aggregation pheromone and insecticide on Le. infantum transmission Lu. longipalpis had been continuously exposed to insecticide for 30 months. The objective of this study was to determine the effect of continuous exposure to the insecticides used in the trial on the susceptibility of Lu. longipalpis population.MethodsDuring the trial the sand flies had been exposed to either lambda-cyhalothrin [pheromone + residual insecticide spray (PI)], deltamethrin [dog collars (DC)] or no insecticide [control (C)], for 30 months (November 2012 to April 2015). The insecticide treatment regime was kept in place for an additional 12 months (May 2015-April 2016) during this susceptibility study. Sand flies collected from the field were exposed to WHO insecticide-impregnated papers cyhalothrin (0.05%), deltamethrin (0.5%) and control (silicone oil) in a modified WHO insecticide exposure trial to determine their susceptibility.ResultsWe collected 788 Lu. longipalpis using CDC-light traps in 31 municipalities across the three trial arms. Probit analysis showed that the knockdown times (KDTs) of Lu. longipalpis collected from the lambda-cyhalothrin exposed PI-arm [KDT50: 31.1 min, confidence interval (CI): 29.6–32.6 and KDT90: 44.2 min, CI: 42.1–46.7] were longer than the KDTs from the non-insecticide-treated C-arm (KDT50: 26.3 min, CI: 25.1–27.6 and KDT90: 38.2, CI: 36.5–40.2) (no-overlapping 95% CIs). KDTs of Lu. longipalpis collected from the deltamethrin exposed DC-arm had similar values (KDT50: 13.7 min, CI: 10.1–16.2 and KDT90: 26.7 min, CI: 21.8–30.6) to those for the C-arm (KDT50: 13.5 min; CI: 12.2–14.8 and KDT90: 23.2 min, CI: 21.4–25.4) (overlapping CIs). The wild-caught unexposed Lu. longipalpis (C-arm), took approximately twice as long to knock down as laboratory-colonised specimens for both insecticides.ConclusionsOur study reveals slight changes in KDT, in sand flies after prolonged exposure to lambda-cyhalothrin in the presence of pheromone. These changes are not considered to have reached the reference levels indicative of resistance in sand flies suggesting that pheromone and insecticide treatment at the level indicated in this study do not constitute a significant risk of increased insecticide resistance. Prolonged exposure to deltamethrin in dog collars did not result in changes to KDT.Electronic supplementary materialThe online version of this article (10.1186/s13071-019-3364-4) contains supplementary material, which is available to authorized users.

Significant reduction in abundance of peridomestic mosquitoes (Culicidae) and Culicoides midges (Ceratopogonidae) after chemical intervention in western São Paulo, Brazil

“…In total, 345 observations of mosquitoes and midges from 1,035 trapping days, and 280 houses were recorded in all 42 study clusters (Table 1). Apart from sand ies [18,19], no other haematophagous Diptera were captured in su cient numbers to be considered in this study.…”

Insecticide-impregnated netting as a potential surface treatment: an alternative to insecticide spraying for control of the leishmaniasis vector Lutzomyia longipalpis (Diptera: Psychodidae)?

“…A trial of synthetic (±)-9-methylgermacrene-B [25] formulated in a long-lasting controlled release device [26,27] co-located with microencapsulated l-cyhalothrin in chicken roosting sites signi cantly reduced Lu. longipalpis densities, canine Leishmania parasite infection incidence, tissue loads and canine seroconversion incidence [23] indicating the potential of this strategy for reducing disease incidence however replacing the sprayed insecticide application with a netting application could improve the cost of the application and therefore coverage.…”

“…The use of synthetic sex/aggregation pheromone in insecticide treated sites overcomes the disruptive effect of the insecticide by continuing to attract female and male sand ies [19,20] and a controlled release formulation of the pheromone can attract Lu. longipalpis for up to 12 weeks [21] greatly extending the lethal effect of the insecticide [22,23]. A trial of the synthetic sex/aggregation, (S)-9methylgermacrene-B [24], formulated in a long-lasting controlled release device [20,21] co-located with microencapsulated l-cyhalothrin in chicken roosting sites signi cantly reduced Lu.…”

Synthetic sex-aggregation pheromone of Lutzomyia longipalpis, the South American sand fly vector of Leishmania infantum, attracts males and females over long-distance

“…Sand fly sex-aggregation pheromones and other semiochemicals offer new opportunities for vector monitoring and control through the deployment of novel trapping and other intervention strategies [ 19 , 22 , 23 ]. A cluster-randomised control trial (RCT) of synthetic ( ± )-9-methylgermacrene-B [ 24 ] formulated in a long-lasting controlled release device [ 25 , 26 ] co-located with sprayed microencapsulated λ-cyhalothrin in chicken roosting sites significantly reduced Lu .…”