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. 2020 Oct 27;13(1):531.
doi: 10.1186/s13071-020-04406-6.

Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018

Kauara Brito Campos  1   2 , Ademir Jesus Martins  3 , Cynara de Melo Rodovalho  3 , Diogo Fernandes Bellinato  3 , Luciana Dos Santos Dias  3 , Maria de Lourdes da Graça Macoris  4 , Maria Teresa Macoris Andrighetti  4 , José Bento Pereira Lima  5 , Marcos Takashi Obara  2
Affiliations

Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018

Kauara Brito Campos et al. Parasit Vectors. .

Abstract

Background: Chemical 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.

Methods: The 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.

Results: Susceptibility 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).

Conclusions: The 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.

Keywords: Aedes aegypti; Arboviruses; Insecticide resistance; Juvenile hormones; Organophosphate insecticides.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Map of Brazil showing the municipalities participating in the 2017–2018 Aedes aegypti pyriproxyfen and malathion susceptibility monitoring round. The numbers in red represent state capitals. The continuous lines in Brazilian territory indicate different states
Fig. 2
Fig. 2
Map of Brazil displaying the results of the IGR pyriproxyfen resistance evaluation for Aedes aegypti populations, 2017–2018. Green circles or orange diamonds represent localities where populations were susceptible or suggested resistance (IE < 98%) was noted, respectively. The states of Bahia (BA) and Ceará (CE) are highlighted and the municipalities presenting suggested resistance populations are indicated
Fig. 3
Fig. 3
Determination of the malathion diagnostic-dose (DD) in Aedes aegypti, Rockefeller strain. a Mortality throughout the exposure period to bottles coated inside with different doses. b Three additional independent trials with DD set at 20 µg/ml, resulting in 100% mortality in 30 min. The red arrow highlights the 30 min mark
Fig. 4
Fig. 4
Map of Brazil displaying the results of the organophosphate malathion resistance evaluation for Aedes aegypti populations, 2017–2018. Diagnostic-dose tests employed a 20 µg/bottle (a) or 50 µg/bottle dose (b). Green circles, orange diamonds or red triangles represent localities where populations were considered susceptible, with suggested resistance or with confirmed resistance, respectively
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