Assessing the susceptibility to permethrin and deltamethrin of two laboratory strains of Phlebotomus perniciosus from Madrid region, Spain

Abstract

Leishmania infantum is a protozoan causing cutaneous and visceral leishmaniasis in several regions of the world, including the Mediterranean basin. Phlebotomus perniciosus is one of the most important vectors of leishmaniasis in the countries of the western Mediterranean basin. Sand fly vector control by insecticides remains a useful tool in the framework of leishmaniasis control programs. Pyrethroids are the most widely used class of insecticides for sand fly control. There is currently a lack of information on the insecticide susceptibility and discriminating concentrations (DCs) of P. perniciosus. The aim of this study was to determine lethal concentrations (LC50, LC95, and LC99) and DCs of deltamethrin and permethrin against two strains of P. perniciosus from Madrid region (Spain). According to WHO tube bioassay protocol 24-h mortality obtained after 1-h exposure to deltamethrin (0.0003%, 0.001%, 0.003%, 0.01%, 0.03%, and 0.1%) and permethrin (0.003%, 0.01%, 0.03%, 0.1%, 0.3%, and 1%) was recorded. The LC50, LC95, and LC99 as well as their respective 95% confidence intervals values were calculated from the baseline data using maximum probability estimates of parameters and binary logistic regression analysis (QCal software). The 100% mortality was recorded from 0.01% of deltamethrin for both P. perniciosus strains and from 0.1% and 0.3% permethrin for Fuenlabrada and Boadilla strains, respectively. Final DCs of deltamethrin and permethrin of each P. perniciosus strain were determined based on setting this parameter at twice the minimum concentration of insecticide that kills 99% (LC99) at the following percentages: Fuenlabrada strain (0.0582% deltamethrin and 0.2648% permethrin) and Boadilla strain (0.0406% deltamethrin and 0.2446% permethrin). The results indicate that both P. perniciosus strains are susceptible to deltamethrin and permethrin and can be used in susceptibility tests, although Boadilla strain offers more consistent results. Due to the scarce existing literature on insecticide DCs for sand flies and the different current procedures to determine their susceptibility to insecticides it is a priority to multiply efforts in order to develop standards for monitoring insecticide resistance in sand flies.