Assessment of the Susceptibility Status of Aedes aegypti (Diptera: Culicidae) Populations to Pyriproxyfen and Malathion in a National Wide Monitoring of Insecticide Resistance in Brazil, 2017-2018
Background: In Brazil chemical control has been used since 1985. For the effectiveness of chemical control, it is essential to monitor the vector susceptibility to insecticides. This study aimed to describe bioassays standardization and to determine the susceptibility profile of Ae. aegypti populations to the products in use malathion and pyriproxyfen on national scale between 2017 and 2018, and to discuss the observed results impact in arboviruses control.Methods: The diagnostic-doses (DD) of
... stic-doses (DD) of pyriproxyfen and malathion were determined as the double of the inhibition of adult emergence (EI) and lethal doses for 99% of the Rockefeller reference strain, respectively. For the monitoring of natural populations, collections were performed in 132 Brazilian cities, through egg traps. Colonies were raised in the laboratory for one or two generations (F1 or F2) and submitted to susceptibility tests with larvae exposed to DD of pyriproxyfen (0.03 µg/L) and adults with the malathion DD herein obtained (20 µg), in addition to the World Health Organization (WHO) indicated DD (50 µg) in bottle assay. Dose-response bioassays with pyriproxyfen were performed with populations which did not achieved 98% EI in the DD assays. Results: Alteration of susceptibility to pyriproxyfen was recorded in 6 (4.5%) Ae. aegypti populations, with Resistance Ratio RR95 from 1.51 to 3.58. These populations were concentrated in Bahia and Ceará states. For malathion, 73 (55,3%) populations distributed all over the country were resistant when exposed to the local DD 20µg/bottle. On the other hand, no one population was resistant, and only 10 (7,6%) populations were considered with decreased susceptibility (mortality ratio between 90 and 98%) when the WHO DD (50 µg/bottle was used). These populations are in the 8 from 27 states.Conclusions: We evidenced the feasibility of conducting an insecticide resistance monitoring action at a national wide scale, employing standardized and strongly coordinated sampling methods and laboratory bioassays. We for the first time identified Brazilian Ae. aegypti populations with decreased susceptibility to pyriproxyfen. Local DD for malathion was more sensitive than the WHO DD to early detect decrease in susceptibility.