Frequency of the Val1016Ile mutation on the kdr gene in Aedes aegypti (Diptera: Culicidae) in south Brazil

Spatial Distribution of Pyrethroid Resistance and kdr Mutations in Aedes aegypti from La Guajira, Colombia

Dengue, chikungunya, and Zika are of great concern to the public health of Colombia. One of the main control strategies for these diseases is the application of insecticides directed at the Aedes aegypti vector. However, insecticide resistance has been increasingly recorded in the country, making control measures difficult. Here, we evaluated the resistance profiles for pyrethroids in populations of Ae. aegypti from La Guajira, Colombia. The frequency (diagnostic dose, DD) and intensity (2×, 5×, and 10× DD) of resistance to permethrin, deltamethrin, and lambda-cyhalothrin were determined in 15 populations of Ae. aegypti from La Guajira, Colombia, using the bottle bioassay. The kdr mutations V1016I, F1534C, and V410L, were identified, and their allele and genotype frequencies were calculated. Finally, the mortality values for the analyzed pyrethroids were interpolated following the IDW method for predicting pyrethroid resistance. The populations of Ae. aegypti showed a high frequency of resistance to permethrin with a low to moderate intensity, which was associated with the triple-resistant haplotype LL410/II1016/CC1534. They remain susceptible to deltamethrin and, in some populations, expressed the risk of developing resistance to lambda-cyhalothrin.

Larvicidal Activity of Essential Oils From Piper Species Against Strains of Aedes aegypti (Diptera: Culicidae) Resistant to Pyrethroids

The continuous and indiscriminate use of insecticides has been responsible for the emergence of insecticide resistant vector insect populations, especially in Aedes aegypti. Thus, it is urgent to find natural insecticide compounds with novel mode of action for vector control. The goal of this study was to investigate the larvicidal activity of essential oils (EOs) from Piper species against A. aegypti characterized as resistant and susceptible strains to pyrethroids. The EOs from leaves of 10 Piper species were submitted to the evaluation of larvicidal activity in populations of A. aegypti in agreement with the (World Health Organization, 2005) guidelines. The resistance of the strains characterized by determining the lethal concentrations (LCs) with the insecticide deltamethrin (positive control). The major compounds of the EOs from Piper species was identified by GC-MS. The EOs from Piper aduncum, P. marginatum, P. gaudichaudianum, P. crassinervium, and P. arboreum showed activity of up to 90% lethality at 100 ppm (concentration for screening). The activities of the EOs from these 6 species showed similar LCs in both susceptible strain (Rockefeller) and resistant strains (Pampulha and Venda Nova) to pyrethroids. The major compounds identified in the most active EO were available commercially and included β-Asarone, (E)-Anethole, (E)-β-Caryophyllene, γ-Terpinene, p-Cymene, Limonene, α-Pinene, and β-Pinene. Dillapiole was purified by from EO of P. aduncum. The phenylpropanoids [Dillapiole, (E)-Anethole and β-Asarone] and monoterpenes (γ-Terpinene, p-Cymene, Limonene, α-Pinene, and β-Pinene) showed larvicidal activity with mortality between 90 and 100% and could account for the toxicity of these EOs, but the sesquiterpene (E)-β-Caryophyllene, an abundant component in the EOs of P. hemmendorffii and P. crassinervium, did not show activity on the three populations of A. aegypti larvae at a concentration of 100 ppm. These results indicate that Piper's EOs should be further evaluated as a potential larvicide, against strains resistant to currently used pesticides, and the identification of phenylpropanoids and monoterpenes as the active compounds open the possibility to study their mechanism of action.

Chronology of sodium channel mutations associated with pyrethroid resistance in Aedes aegypti

Aedes aegypti is the primary mosquito vector of dengue, yellow fever, Zika and chikungunya. Current strategies to control Ae. aegypti rely heavily on insecticide interventions. Pyrethroids are a major class of insecticides used for mosquito control because of their fast acting, highly insecticidal activities and low mammalian toxicity. However, Ae. aegypti populations around the world have begun to develop resistance to pyrethroids. So far, more than a dozen mutations in the sodium channel gene have been reported to be associated with pyrethroid resistance in Ae. aegypti. Co-occurrence of resistance-associated mutations is common in pyrethroid-resistant Ae. aegypti populations. As global use of pyrethroids in mosquito control continues, new pyrethroid-resistant mutations keep emerging. In this microreview, we compile pyrethroid resistance-associated mutations in Ae. aegypti in a chronological order, as they were reported, and summarize findings from functional evaluation of these mutations in an in vitro sodium channel expression system. We hope that the information will be useful for tracing possible evolution of pyrethroid resistance in this important human disease vector, in addition to the development of methods for global monitoring and management of pyrethroid resistance in Ae. aegypti.

Insecticide resistance levels and mechanisms in Aedes aegypti populations in and around Ouagadougou, Burkina Faso

BACKGROUND

Recent outbreaks of dengue and other Aedes aegypti-borne arboviruses highlight the importance of a rapid response for effective vector control. Data on insecticide resistance and underlying mechanisms are essential for outbreak preparedness, but are sparse in much of Africa. We investigated the levels and heterogeneity of insecticide resistance and mechanisms of Ae. aegypti from contrasting settings within and around Ouagadougou, Burkina Faso.

METHODOLOGY/PRINCIPAL FINDINGS

Bioassays were performed on larvae and adults to diagnose prevalence of resistance, and to assess levels where resistance was detected. Investigation of resistance mechanisms was performed using synergist bioassays, knockdown resistance (kdr) target site mutation genotyping and quantitative PCR expression analysis of candidate P450 genes. Larval dose-response assays indicated susceptibility to the organophosphates tested. Adult females were also susceptible to organophosphates, but resistance to carbamates was suspected in urban and semi-urban localities. Females from all localities showed resistance to pyrethroids but resistance prevalence and level were higher in urban and especially in semi-urban areas, compared to the rural population. Environment was also associated with susceptibility: adults reared from larvae collected in tires from the semi-urban site were significantly less resistant to pyrethroids than those collected from large outdoor drinking water containers ('drums'). Susceptibility to both pyrethroids tested was largely restored by pre-exposure to Piperonyl Butoxide (PBO), suggesting a strong metabolic basis to resistance. The 1534C kdr mutation was nearly fixed in semi-urban and urban areas but was far less common in the rural area, where the 1016I kdr mutation frequency was also significantly lower. P450 gene analysis detected limited over-expression of single candidates but significantly elevated average expression in the semi-urban site compared to both a susceptible laboratory colony, and females from the other collection sites.

CONCLUSIONS/SIGNIFICANCE

Our results reveal pyrethroid resistance and paired kdr mutations in both urban and semi-urban sites at levels that are unprecedented for mainland Africa. The combination of target site and metabolic mechanisms is common in Ae. aegypti populations from other continents but is a worrying finding for African populations. However, organophosphate insecticides are still active against both larvae and adults of Ae. aegypti, providing useful insecticidal options for control and resistance management.

High frequencies of F1534C and V1016I kdr mutations and association with pyrethroid resistance in Aedes aegypti from Somgandé (Ouagadougou), Burkina Faso

BACKGROUND

Resistance to pyrethroid insecticides involving kdr mutations is widespread in Aedes aegypti (L.) (Diptera: Culicidae) and potentially could impact control efforts in endemic countries. Dengue cases had been sporadic in Burkina Faso for over a decade prior to the 2016-2017 outbreak that resulted in 15,074 suspected cases and 36 deaths, mainly in Ouagadougou. These outbreaks highlighted the lack of information on numerous aspects of the biology, behaviour and insecticide status of local dengue vector populations that are fundamental to vector control.

RESULTS

We investigated the insecticide resistance profiles and the kdr mutations involved in pyrethroid resistance of Ae. aegypti from Somgandé, a district of Ouagadougou. WHO bioassays revealed that the local Ae. aegypti populations were highly resistant to pyrethroids with mortalities of 15% for permethrin and 37% for deltamethrin. Resistance to carbamates was also detected with mortalities of 55% for propoxur and 90% for bendiocarb, but high mortalities (> 97%) to organophosphates (malathion and fenitrothion) indicated susceptibility. Allele-specific PCR and voltage-gated sodium channel gene sequencing showed a very high frequency (97%) of the F1534C kdr allele whilst the V1016I kdr mutation frequency was 46%. Association of dual-locus kdr mutations was detected for permethrin resistance.

CONCLUSION

We conclude that in this locality of Burkina Faso, Ae. aegypti is resistant to pyrethroid and carbamate insecticides but remains susceptible to organophosphates, providing useful information for possible future control.

A Point Mutation V419L in the Sodium Channel Gene from Natural Populations of Aedes aegypti Is Involved in Resistance to λ-Cyhalothrin in Colombia

Resistance to pyrethroids in mosquitoes is mainly caused by target site insensitivity known as knockdown resistance (kdr). In this work, we examined the point mutations present in portions of domains I, II, III, and IV of the sodium channel gene in Aedes aegypti mosquitoes from three Colombian municipalities. A partial region coding for the sodium channel gene from resistant mosquitoes was sequenced, and a simple allele-specific PCR-based assay (AS-PCR) was used to analyze mutations at the population level. The previously reported mutations, V1016I and F1534C, were found with frequencies ranging from 0.04 to 0.41, and 0.56 to 0.71, respectively, in the three cities. Moreover, a novel mutation, at 419 codon (V419L), was found in Ae. aegypti populations from Bello, Riohacha and Villavicencio cities with allelic frequencies of 0.06, 0.36, and 0.46, respectively. Interestingly, the insecticide susceptibility assays showed that mosquitoes from Bello were susceptible to λ-cyhalothrin pyrethroid whilst those from Riohacha and Villavicencio were resistant. A positive association between V419L and V1016I mutations with λ-cyhalothrin resistance was established in Riohacha and Villavicencio. The frequency of the F1534C was high in the three populations, suggesting that this mutation could be conferring resistance to insecticides other than λ-cyhalothrin, particularly type I pyrethroids. Further studies are required to confirm this hypothesis.