Abstract
BackgroundChemical mosquito control using malathion has been applied in Brazil since 1985. To obtain chemical control effectiveness, vector susceptibility insecticide monitoring is required. This study aimed to describe bioassay standardizations and determine the susceptibility profile of Ae. aegypti populations to malathion and pyriproxyfen, used on a national scale in Brazil between 2017 and 2018, and discuss the observed impacts in arbovirus control.MethodsThe diagnostic-doses (DD) of pyriproxyfen and malathion were determined as the double of adult emergence inhibition (EI) and lethal doses for 99% of the Rockefeller reference strain, respectively. To monitor natural populations, sampling was performed in 132 Brazilian cities, using egg traps. Colonies were raised in the laboratory for one or two generations (F1 or F2) and submitted to susceptibility tests, where larvae were exposed to the pyriproxyfen DD (0.03 µg/l) and adults, to the malathion DD determined in the present study (20 µg), in addition to the one established by the World Health Organization (WHO) DD (50 µg) in a bottle assay. Dose-response (DR) bioassays with pyriproxyfen were performed on populations that did not achieve 98% EI in the DD assays.ResultsSusceptibility alterations to pyriproxyfen were recorded in six (4.5%) Ae. aegypti populations from the states of Bahia and Ceará, with Resistance Ratios (RR95) ranging from 1.51 to 3.58. Concerning malathion, 73 (55.3%) populations distributed throughout the country were resistant when exposed to the local DD 20 µg/bottle. On the other hand, no population was resistant, and only 10 (7.6%) populations in eight states were considered as exhibiting decreased susceptibility (mortality ratios between 90 and 98%) when exposed to the WHO DD (50 µg/bottle).ConclusionsThe feasibility of conducting an insecticide resistance monitoring action on a nation-wide scale was confirmed herein, employing standardized and strongly coordinated sampling methods and laboratory bioassays. Brazilian Ae. aegypti populations exhibiting decreased susceptibility to pyriproxyfen were identified. The local DD for malathion was more sensitive than the WHO DD for early decreased susceptibility detection.
Highlights
Chemical mosquito control using malathion has been applied in Brazil since 1985
The Brazilian Ministry of Health (MoH) provides insecticides pre-qualified by the World Health Organization (WHO) to all Brazilian states for the chemical control of Ae. aegypti
A total of 146 urban Brazilian cities were selected to evaluate Ae. aegypti susceptibility/resistance to insecticides current employed in official national campaigns throughout the country (Table 1, Fig. 1), based on a geographical representation proposal
Summary
Chemical mosquito control using malathion has been applied in Brazil since 1985. To obtain chemical control effectiveness, vector susceptibility insecticide monitoring is required. Actions against the Aedes (Stegomyia) aegypti (Linnaeus, 1762) are mainly based on chemical and mechanical controls aiming to reduce infestation, while social mobilization, environmental management and legislation protections seeking to maintain environments free of larval breeding sites are applied. The most effective form of vector control is environmental management involving mechanical reservoir removal, arbovirus transmission blocking usually comprises chemical insecticide applications, aiming at rapidly reducing mosquito populations [2]. The Brazilian Ministry of Health (MoH) provides insecticides pre-qualified by the World Health Organization (WHO) to all Brazilian states for the chemical control of Ae. aegypti. This process ensures that the entire country employs trusted products concerning environmental safety, toxicity and effectiveness [3]. Public health actions used to control Ae. aegypti in Brazil consume an expressive amount of insecticides each year, considering, for example, that about 4136 Brazilian municipalities registered dengue cases from 2014 to 2017 [5]
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