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.

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background:</jats:bold> 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 <jats:italic>Ae. aegypti</jats:italic> 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.<jats:bold>Methods: </jats:bold>The diagnostic-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. <jats:bold>Results:</jats:bold> Alteration of susceptibility to pyriproxyfen was recorded in 6 (4.5%) <jats:italic>Ae. aegypti</jats:italic> populations, with Resistance Ratio RR<jats:sub>95</jats:sub> 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.<jats:bold>Conclusions: </jats:bold>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 <jats:italic>Ae. aegypti</jats:italic> populations with decreased susceptibility to pyriproxyfen. Local DD for malathion was more sensitive than the WHO DD to early detect decrease in susceptibility.</jats:p>

Kdr genotyping in Aedes aegypti from Brazil on a nation-wide scale from 2017 to 2018

“…In Brazil, the most recent nation-wide Ae. aegypti IR monitoring detected several populations resistant to malathion 39 . The Brazilian MoH is currently planning the implementation of an alternative compound comprising a mixture of pyrethroids and clothianidin to be sprayed inside houses, in addition to another compound comprising a mixture of pyrethroids and imidacloprid as an ULV for outdoor areas.…”

“…Field agents installed eggtraps randomly distributed according to the total number of houses in each municipality, as follows: 100, 150, 200 or 300 traps for < 50, 50-200, 200-500 and > 500 thousand houses, respectively. The installation and collection methodology of the eggtraps is described elsewhere 39 . A presential meeting was organized with field-personnel representatives of each state and a video with step-by-step procedures was launched (https ://www.youtu be.com/watch ?v=2w89k agSOK M) in order to ensure that collections were made as homogeneously as possible.…”