Efficacy of orally toxic sugar baits against contact-insecticide resistant culex quinquefasciatus.

In recent years, attractive toxic sugar bait has been used in the mosquito control in nature, and achieved good control effects. However, the current researches about toxic sugar bait did not focus on whether the wild mosquito population used for control is resistant or not. The purpose of this study was to evaluate the effectiveness of the toxic sugar bait against mosquito resistant populations to test the effects of bait on the control of mosquitoes with different levels of resistance. Boric acid, dinotefuran and deltamethrin were separately formulated into toxic sugar bait to test their anti-mosquito activity against Culex quinquefasciatus. Using the sugar baits formulated with boric acid and dinotefuran, the mortality of Cx. quinquefasciatus resistant populations was significantly higher than that of sensitive populations at the same concentration. Conversely, with the use of sugar baits formulated with deltamethrin, the mortality of Cx. quinquefasciatus resistant populations was significantly lower than that of sensitive populations at the same concentration. The results suggested that toxic sugar baits might have a good application prospect in high resistant mosquito management.

First detection of multiple knockdown resistance (kdr)-like mutations in voltage-gated sodium channel using three new genotyping methods in Anopheles sinensis from Guangxi Province, China.

To investigate knockdown resistance (kdr)-like mutations associated with pyrethroid resistance in Anopheles sinensis (Wiedemann, 1828), from Guangxi province, southwest China, a segment of a sodium channel gene was sequenced and genotyped using three new genotyping assays. Direct sequencing revealed the presence of TTG-to-TCG and TG-to-TTT mutations at allele position L1014, which led to L1014S and L1014F substitutions in a few individual and two novel substitutions of N1013S and L1014W in two DNA templates. A low frequency of the kdr allele mostly in the heterozygous state of L1014S and L1014F was observed in this mosquito population. In this study, the genotyping of An. sinensis using three polymerase chain reaction-based methods generated consistent results, which agreed with the results of DNA sequencing. In total, 52 mosquitoes were genotyped using a direct sequencing assay. The number of mosquitoes and their genotypes were as follows: L/L = 24, L/S = 19, L/F = 8, and F/W = 1. The allelic frequency of L1014, 1014S, and 1014F were 72, 18, and 9%, respectively.

Company amplification of estalpha2/estbeta2 and correlation between esterase gene copy number and resistance to insecticides in the field Culex pipiens pallens strains collected from Beijing, China.

Seven field strains of Culex pipiens pallens were evaluated in the summer of 2004 for their susceptibility to three insecticides. Larval bioassays were carried out in accordance with WHO mosquito susceptibility tests. Field samples showed resistance to dichlorvos and propoxur. Low levels of resistance to phoxim were detected compared with the laboratory-susceptible strain. Quantitative analysis showed that co-amplification of estalpha2 and estbeta2 occurred in the seven field Cx. pipiens pallens. However, the levels of transcription of estalpha2/estbeta2 genes in the field strains indicated a 15.9:1 ratio of estbeta32 cDNA over estalpha2 cDNA. Such observed differential transcription of the estalpha2/estbeta2 genes showed that the promoters regulating their expression are independent and of different strengths. Regression analysis of expression level of estalpha2/estbeta2 gene and LC50 value to insecticides showed a significant correlation between expression level ofestalpha2 gene and LC50 value to dichlorvos. However, correlation of estalpha2 gene and LC50 value to propoxur and phoxim, or estbeta2 gene and three kinds of insecticides, was not significant.