Seven F1 strains of Aedes aegypti (L.) were evaluated by bottle bioassay for resistance to the pyrethroids d-phenothrin, permethrin, deltamethrin, λ-cyalothrin, bifenthrin, cypermethrin, α-cypermethrin and z-cypermethrin. The New Orleans strain was used as a susceptible control. Mortality rates after a 1h exposure and following a 24h recovery period were determined. The resistance ratio between the 50% knockdown values (RRKC50) of the F1 and New Orleans strains indicated high levels of knockdown resistance (kdr). The RRKC50 with α-cypermethrin varied from 10–100 among strains indicating high levels of kdr. Most of the strains had moderate resistance to d-phenothrin. Significant but much lower levels of resistance were detected for λ–cyalothrin, permethrin and cypermethrin. For z-cypermethrin and bifenthrin, only one strain exhibited resistance with RRKC50 values of 10- and 21-fold, respectively. None of the strains showed RRKC50 >10 with deltamethrin, and moderate resistance was seen in three strains, while the rest were susceptible. Mosquitoes from all strains exhibited some recovery from all pyrethroids except d-phenothrin. Regression analysis was used to analyze the relationship between RRLC50 and RRKC50. Both were highly correlated (R2 = 0.84 – 0.97) so that the slope could be used to determine how much additional pyrethroid was needed to insure lethality. Slopes ranged from 0.875 for d-phenothrin (RRLC50 ≃ RRKC50) to 8.67 for λ–cyalothrin (~8.5 fold more insecticide needed to kill). Both RRLC50 and RRKC50 values were highly correlated for all pyrethroids except bifenthrin indicating strong cross resistance. Bifenthrin appears to be an alternative pyrethroid without strong cross resistance that could be used as an alternative to the current widespread use of permethrin in Mexico.

The results showed that C1534 frequencies are higher than I1016 frequencies in natural populations of Ae. aegypti in Venezuela, and that deltamethrin selected the C1534 more rapidly than I1016.

Challenges in maintaining high effectiveness of classic vector control in urban areas has renewed the interest in indoor residual spraying (IRS) as a promising approach for Aedes -borne disease prevention. While IRS has many benefits, application time and intrusive indoor applications make its scalability in urban areas difficult. Modifying IRS to account for Ae . aegypti resting behavior, named targeted IRS (TIRS, spraying walls below 1.5 m and under furniture) can reduce application time; however, an untested assumption is that modifications to IRS will not negatively impact entomological efficacy. We conducted a comparative experimental study evaluating the residual efficacy of classically-applied IRS (as developed for malaria control) compared to two TIRS application methods using a carbamate insecticide against a pyrethroid-resistant, field-derived Ae . aegypti strain. We performed our study within a novel experimental house setting (n = 9 houses) located in Merida (Mexico), with similar layouts and standardized contents. Classic IRS application (insecticide applied to full walls and under furniture) was compared to: a) TIRS: insecticide applied to walls below 1.5 m and under furniture, and b) Resting Site TIRS (RS-TIRS): insecticide applied only under furniture. Mosquito mortality was measured eight times post-application (out to six months post-application) by releasing 100 Ae . aegypti females /house and collecting live and dead individuals after 24 hrs exposure. Compared to Classic IRS, TIRS and RS-TIRS took less time to apply (31% and 82% reduction, respectively) and used less insecticide (38% and 85% reduction, respectively). Mortality of pyrethroid-resistant Ae . aegypti did not significantly differ among the three IRS application methods up to two months post application, and did not significantly differ between Classic IRS and TIRS up to four months post application. These data illustrate that optimizing IRS to more efficiently target Ae . aegypti can both reduce application time and insecticide volume with no apparent reduction in entomological efficacy.

Resistance to the insecticides deltamethrin and malathion and the enzymes associated with metabolic resistance mechanisms were determined in four field populations of Aedes aegypti (L.) from western Venezuela during 2008 and 2010 using the bottle assay and the microplate biochemical techniques. For deltamethrin, mortality rates after 1 h exposure and after a 24-h recovery period were determined to calculate the 50% knock-downconcentration (KC50) and the lethal concentration (LC50), respectively. For malathion, mortality was recorded at 24 h to determine the LC50. For deltamethrin, resistance ratios of knock-down resistance and postrecovery were determined by calculating the RRKC50 and RRLC50, comparing the KC50 and LC50 values of the field populations and those of the susceptible New Orleans strain. Knock-down resistance to deltamethrin was moderate in the majority of the populations in 2008 (RRKC50 values were between 5- and 10-fold), and only one population showed high resistance in 2010 (RRKC50 > 10-fold). Moderate and high postrecovery resistance to deltamethrin was observed in the majority of the populations for 2008 and 2010, respectively. There was significantly increased expression of glutathione-S-tranferases and mixed-function oxidases. All populations showed low resistance to malathion in 2008 and 2010 with significantly higher levels of alpha-esterases for 2008 and 2010 and beta-esterases for 2008.

The nucleotide sequence of three single alpha‐globin genes resulting from a rightward 3.7‐kb deletion is described. The alpha genes were isolated from the DNA of three subjects homozygous for this deletion, the first being in addition homozygous for the structural mutation alpha G Philadelphia (genotype ‐alpha G/‐alpha G), the second, heterozygous for this structural mutation (genotype ‐alpha A/‐alpha G) and the third homozygous for an alpha + ‐thalassaemic gene (genotype ‐alpha +thal/‐alpha +thal). The latter subject produced HbH in contrast to the two others. Whereas the two alpha A and alpha G genes are identical to the normal alpha 1‐globin gene (except for the alpha G point mutation), the alpha +thal gene has (i) a deletion of the two nucleotides at position ‐2 and ‐3 preceding the ATG codon, and (ii) a fusion between the 5′ part of the normal alpha 2 gene and the 3′ part of the normal alpha 1 gene. Using a dot‐blot assay, we show that reticulocytes from the HbH subject contain at least as much alpha mRNA as reticulocytes from the two other subjects. In a transient expression system, the alpha +thal gene leads to normally spliced transcripts. We conclude from these data that the defective output of alpha chains by the alpha +thal gene, as evidenced by HbH production, results from a decreased efficiency of alpha‐mRNA translation due to the two nucleotides deletion preceding the AUG codon.

Alterations in life parameters could be due to the accumulation of noxious effects or deleterious genes related to detoxifying enzymes, specifically those coding for mixed-function oxidases, along with the presence of recessive alleles of the V1016I and F1534C mutations, associating deltamethrin resistance with fitness cost in Ae. aegypti. © 2017 Society of Chemical Industry.

Aedes aegypti (L.) is the primary vector of the viruses that cause dengue, Zika, and chikungunya, for which effective vaccines and drugs are still lacking. Current strategies for suppressing arbovirus outbreaks based on insecticide use pose a challenge because of the rapid increase in resistance. The widespread and excessive use of pyrethroid-based insecticides has created a large selection pressure for a kdr-type resistance, caused by mutations in the para gene of the voltage-gated sodium channel (vgsc). Our objective was to evaluate the allelic frequency of natural populations of Ae. aegypti of Mexico at codon 410 of the para gene. Twenty-six Ae. aegypti populations from east and southern Mexico were genotyped for the codon 410 using allele-specific PCR. The frequencies of the L410 allele in Ae. aegypti ranged from 0.10 to 0.99; however, most of the frequencies were in the range of 0.36 to 0.64. The highest frequencies were found in three populations from the state of Veracruz, namely, Minatitlan with 0.99, Poza Rica with 0.82, and Jose Cardel with 0.97, along with populations from Cancun in Quintana Roo with 0.93, Frontera in Tabasco with 0.91, and Ciudad del Carmen in Campeche with 0.86. The frequency of the L410 allele was high in all populations of Ae. aegypti with higher values in populations of the southeast of the country. The knowledge of specific substitutions in vgsc and their interaction to confer resistance is essential to predict and develop future strategies for resistance management in Ae. aegypti in Mexico.

This study showed that high frequencies of kdr mutations V1016I and F1534C are reflected in the results of F-RDT and I-RDT tests. Bioassays in conjunction with the characterization of genetic resistance mechanisms are indispensable in the strategic and rational management of resistance in mosquitoes. © 2018 Society of Chemical Industry.