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

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.

Exploring Conditions for Handling Packing and Shipping Aedes aegypti Males to Support an SIT Field Project in Brazil

“…One crucial factor is the constant pressure of selecting mosquito populations resistant to insecticides, reducing the number of substance options, or increasing the amount used significantly [ 13 , 14 , 15 ]. In the last decade, Brazil has initiated a new chapter, willing to evaluate new approaches to controlling the mosquito population using alternatives [ 16 , 17 ], such as genetically modified organisms for population suppression [ 18 , 19 ]; mosquito population replacement carrying a symbiont [ 20 , 21 , 22 ]; the use pyriproxyfen in dissemination stations increasing juvenile mortality [ 23 , 24 ]; and at last, the use of sterile males, as proposed in this study [ 16 , 25 ].…”

Brazilian Populations of Aedes aegypti Resistant to Pyriproxyfen Exhibit Lower Susceptibility to Infection with Zika Virus

“…Three years later, Ae. aegypti populations resistant to the larvicide PPF were detected in some cities in the same region [ 24 ], which is predicted to undermine the control of mosquito-borne arboviruses. However, some authors have suggested that IR may also impinge on mosquito control through alterations in vector traits, especially vector longevity, competence, and behavior [ 37 ].…”

“…aegypti in public health throughout Brazil since 2014, largely attributable to insecticide resistance (IR) in Ae. aegypti to other insecticides, including pyrethroids and organophosphates [ 23 , 24 ]. The most studied mechanisms responsible for the evolution of resistance are increased activity of detoxifying enzymes and modification of the insecticide target site.…”

“…Assessment of the susceptibility status of 123 Ae. aegypti populations collected throughout Brazil between 2017 and 2018 detected IR to PPF in populations from municipalities in the states of Bahia and Ceará, Northeast region, for the first time in Brazil [ 24 ]. It is known that IR can affect vector control efforts and epidemic prevention; however, few studies have assessed the influence of IR on Ae.…”

Susceptibility of South Texas Aedes aegypti to Pyriproxyfen

“…This emphasizes the importance of vector control activities to deliver an adequate dose of insecticide and that failure to do so could enhance the observed resistance. Surveillance for the development of resistance for pyriproxyfen is important as there have been reports of resistance elsewhere in the world [ 24 , 25 ].…”