Insecticide resistance in Aedes aegypti populations from Ceará, Brazil.

Abstract

BACKGROUND:

Organophosphates and pyrethroids are used widely in Brazil to control Aedes aegypti, the main vector of dengue viruses, under the auspices of the National Programme for Dengue Control. Resistance to these insecticides is widespread throughout Brazil. In Ceará the vector is present in 98% of districts and resistance to temephos has been reported previously. Here we measure resistance to temephos and the pyrethroid cypermethrin in three populations from Ceará and use biochemical and molecular assays to characterise resistance mechanisms.

RESULTS:

Resistance to temephos varied widely across the three studied populations, with resistance ratios (RR(95)) of 7.2, 30 and 192.7 in Juazeiro do Norte, Barbalha and Crato respectively. The high levels of resistance detected in Barbalha and Crato (RR(95) ≥ 30) imply a reduction of temephos efficacy, and indeed in simulated field tests reduced effectiveness was observed for the Barbalha population. Two populations (Crato and Barbalha) were also resistant to cypermethrin, whilst Juazeiro do Norte showed only an altered susceptibility. The Ile1011Met kdr mutation was detected in all three populations and Val1016Ile in Crato and Juazeiro do Norte. 1011Met was significantly associated with resistance to cypermethrin in the Crato population. Biochemical tests showed that only the activity of esterases and GSTs, among the tested detoxification enzymes, was altered in these populations when compared with the Rockefeller strain.

CONCLUSIONS:

Our results demonstrate that two A. aegypti populations from Ceará are under strong selection pressure by temephos, compromising the field effectiveness of this organophosphate. Our results also provide evidence that the process of reducing resistance to this larvicide in the field is difficult and slow and may require more than seven years for reversal. In addition, we show resistance to cypermethrin in two of the three populations studied, and for the first time the presence of the allele 1016Ile in mosquito populations from northeastern Brazil. A significant association between 1011Met and resistance was observed in one of the populations. Target-site mechanisms seem not to be implicated in temephos resistance, reinforcing the idea that for the studied populations, detoxification enzymes most likely play a major role in the resistance to this insecticide.

• Authors: Estelita Pereira Lima, Marcelo Henrique Santos Paiva, Ana Paula de Araújo, Ellyda Vanessa Gomes da Silva, Ulisses Mariano da Silva, Lúcia Nogueira de Oliveira, Antonio Euzébio G Santana, Clarisse Nogueira Barbosa, Clovis C de Paiva Neto, Marilia O F Goulart, Craig Stephen Wilding, Constância Flávia Junqueira Ayres, Maria Alice V de Melo Santos
• Journal: Parasites & vectors (Parasit Vectors) Vol. 4 Pg. 5 (Jan 12 2011) ISSN: 1756-3305 [Electronic] England
• PMID: 21226942 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Insect Proteins
• Insecticides
• Pyrethrins
• cypermethrin
• Temefos

Topics

• Aedes (drug effects, genetics)
• Alleles
• Animals
• Brazil
• Disease Vectors
• Female
• Insect Proteins (genetics)
• Insecticide Resistance
• Insecticides (pharmacology)
• Male
• Mutation, Missense
• Pyrethrins (pharmacology)
• Selection, Genetic
• Temefos (pharmacology)