Abstract
The mosquito Aedes aegypti is the primary vector of different arboviruses and represents a major public health problem. Several Brazilian populations of Ae. aegypti have developed resistance to temephos, the most used organophosphate larvicide. New tools which are less harmful to the environment and safer for humans are becoming increasingly important to control this insect vector. Spinosad, an aerobic fermentation product of a soil actinobacteria, has a favorable environmental profile. It presents selective insecticide properties, a mechanism of action that differs from those of many synthetic chemical insecticides. The toxicity of spinosad and temephos to Aedes aegypti populations from Brazil, which were previously exposed to temephos, were investigated in this study. Larval susceptibility (LC50) to temephos varied from 3μg/L for Rockefeller up to 260 μg/L for Santana do Ipanema field derived population. Larval susceptibility (LC50) to spinosad varied from 23μg/L for Rockefeller up to 93μg/L for Marilia field derived population. In addition, a semi-field trial was performed to evaluate spinosad (NatularTM DT) initial efficacy and persistence toward four field-derived lineages and the Rockefeller lineage, used as an internal control. Spinosad was tested at 0.5mg active ingredient/L in 200L capacity water tanks. Mortality was recorded each 24 hours after exposition and tanks were further recolonized once per week with mortality being recorded daily for eight weeks. Spinosad provided a level equal or superior to 80% mortality during a seven to eight week evaluation period. The assessed populations did not present cross-resistance between spinosad and temephos in laboratory conditions. It demonstrates that spinosad may be a promising larvicide for the control of Ae. aegypti, especially for populations in which resistance to temephos has been detected.
Highlights
The Aedes aegypti (Linnaeus, 1762) mosquito, widely distributed in the tropical and subtropical regions of the planet, is highly adapted to the urban environment and is often found within and around households [1,2,3]
These materials were collected by the municipalities’ health secretaries and sent to the Laboratorio de Fisiologia e Controle de Artropodes Vetores (Fiocruz, Rio de Janeiro) by the Brazilian Health Ministry.The females were reared as follow: eggs collected in the field were hatched in the laboratory in order to obtain 1st instar larvae that developed to the adults of the parental generation of these strains
The lethal concentration (LC50) of the larvae bioassays for spinosad ranged from 23μg/L for the susceptilble Rockefeller reference lineage up to 82μg/L for the field populations
Summary
The Aedes aegypti (Linnaeus, 1762) mosquito, widely distributed in the tropical and subtropical regions of the planet, is highly adapted to the urban environment and is often found within and around households [1,2,3] It is the main vector of dengue viruses and can play a role as vector of yellow fever virus in the urban cycle [4], which are considered two of the most. Spinosad toxicity in Aedes aegypti from Brazil important viral diseases transmitted by arthropods [5]. This insect is a potential vector transmitter of Chikungunya virus and Zika virus [6,7,8]. Public health measures focus mainly on the vector control [9,10]
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