The susceptibility of Aedes aegypti populations displaying temephos resistance to Bacillus thuringiensis israelensis: a basis for management.
BACKGROUND
Aedes aegypti is the vector of dengue virus, and its control is essential to prevent disease transmission. Among the agents available to control this species, biolarvicides based on Bacillus thuringiensis serovar israelensis (Bti) are an effective alternative to replace the organophosphate temephos for controlling populations that display resistance to this insecticide. The major goal of this study was to determine the baseline susceptibility of Brazilian Ae. aegypti populations to Bti, taking into account their background in terms of larvicide exposure, status of temephos resistance and the level of activity of detoxifying enzymes involved in metabolic resistance to insecticides.


METHODS
Population samples were established under insectarium conditions. Larval susceptibility to temephos and Bti was evaluated through bioassays and lethal concentrations of these compounds were determined. Biochemical assays were performed to determine the specific activity of five detoxifying enzymes in these samples.


RESULTS
Fourteen populations were characterized and, except for one case, all displayed resistance to temephos. Most populations were classified as highly resistant. The populations also showed increased activity of one or more detoxifying enzymes (glutathione-S-transferases, esterases and mixed function oxidases), regardless of their temephos resistance status. All populations analyzed were susceptible to Bti, and the lethal concentrations were similar to those detected in two laboratory susceptible colonies. The response to Bti showed little variation. A maximum resistance ratio of 2.1 was observed in two untreated populations, while in two Bti-treated populations, the maximum resistance ratio was 1.9. No positive correlation was found between temephos resistance, increased activity of detoxifying enzymes, and susceptibility to Bti.


CONCLUSIONS
Data from this study show that all populations were susceptible to Bti, including twelve untreated and two treated populations that had been exposed to this agent for more than ten years. The temephos resistance and increased activity of detoxifying enzymes observed in thirteen populations was not correlated with changes in susceptibility to Bti. Our data show a lack of cross-resistance between these two compounds; thus, Bti can be used in an integrated control program to fight Ae. aegypti and counteract the temephos resistance that was found among all populations analyzed.
Ana Paula
AP
Araújo
Diego Felipe
DF
Araujo Diniz
Elisama
E
Helvecio
Rosineide Arruda
RA
de Barros
Cláudia Maria Fontes
CM
de Oliveira
Constância Flávia Junqueira
CF
Ayres
Maria Alice Varjal
MA
de Melo-Santos
Lêda Narcisa
LN
Regis
Department of Entomology, Centro de Pesquisas Aggeu Magalhães-FIOCRUZ, Recife, PE 50670-420, Brazil. mhneves@cpqam.fiocruz.br.
Maria Helena Neves Lobo
MH
Silva-Filha
D000330:Aedes / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D000818:Animals; D001413:Bacillus thuringiensis / Q000254:growth & development*; D007303:Insect Vectors; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology; D010572:Pest Control, Biological / Q000379:methods*; D016019:Survival Analysis; D000002:Temefos / Q000494:pharmacology
D007306:Insecticides; D000002:Temefos