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Objective. To determine the abundance and geographic distribution of the main malaria vectors, which are influenced by habitat characteristics and ecological factors that directly impact adult density and the dynamics of malaria transmission in Mexico. Materials and methods. Samples of larvae were collected from 19 states in Mexico. Each larval habitat was characterized in situ determining the following param­eters: water depth, turbidity, percentage of vegetation cover, amount of detritus, presence of algae, light intensity, type of vegetation, amount of predators, habitat stability, altitude, and hydrologic type. Results. A total of 21 687 larvae cor­responding to 13 anopheline species were obtained from 149 aquatic habitats. The most abundant species were Anopheles pseudopunctipennis (52.91%), An. albimanus (39.14%) and An. franciscanus (5.29%). The multiple logistic regression analysis showed a negative association between An. pseudopunctipennis and water turbidity (ß=-1.342; Wald=6.122; p=0.013) and the amount of detritus (ß=-2.206; Wald=3.642; p=0.050). While in An. albimanus, there was a significant positive association with water turbidity (ß=1.344; Wald=4.256; p=0.039), a negative correlation was found with the altitude (ß=-3.445; Wald=5.407; p =0.020). The highest mosquito species diver­sity index was found in Chiapas (Fisher’s α=1.20) and the lowest diversity in Chihuahua (Fisher’s α=0.26). The great­est richness was found in streams (n=11). Conclusions. The two most abundant species were: An. albimanus and An pseudopunctipennis. Detailed knowledge of the distribution and characteristics of their larval habitats will be useful for the effective implementation of control strategies in Mexico.

Objective. The feasibility of the use of WHO impregnated paper and biochemical assays to determine lethal concentra­tions (LC50 and LC99) and insecticide metabolic enzyme levels of Triatoma dimidiata. Materials and methods. LC50 and LC99 were calculated with WHO papers impregnated at differ­ent concentrations of malathion, propoxur and deltamethrin; the percentage of insensitive acetylcholinesterase (iAChE); and the levels of esterases, glutathione S-transferases, and monooxygenases in laboratory nymphs of the first stage (5 to 7 days), were undertaken using the WHO biochemical assays. Results. Respectively the LC50 and LC99 μg/cm2 obtained for malathion were 43.83 and 114.38, propoxur 4.71 and 19.29, and deltamethrin 5.80 and 40.46. A 30% of the population had an iAChE, and only a few individuals had high P450 and β-eterase levels. Conclusion. Impregnated papers and bio­chemical tests developed by WHO for other insects, proved to be feasible methods in monitoring insecticide resistance and metabolic enzymes involved in T. dimidiata.

BackgroundInsecticide use continues as the main strategy to control Aedes aegypti, the vector of dengue, Zika, chikungunya, and yellow fever. In the city of Tapachula, Mexico, mosquito control programs switched from pyrethroids to organophosphates for outdoor spatial spraying in 2013. Additionally, the spraying scheme switched from total coverage to focused control, prioritizing areas with higher entomological-virological risk. Five years after this strategy had been implemented, we evaluated the status and variability of insecticide resistance among Ae. aegypti collected at 26 sites in Tapachula.Methodology/principal findingsWe determined the lethal concentrations at 50% of the tested populations (LC50) using a bottle bioassay, and then, we calculated the resistance ratio (RR) relative to the susceptible New Orleans strain. Permethrin and deltamethrin (pyrethroids), chlorpyrifos and malathion (organophosphates), and bendiocarb (carbamate) were tested. The frequencies of the substitutions V1016I and F1534C, which are in the voltage-gated sodium channel and confer knockdown-resistance (kdr) to pyrethroid insecticides, were calculated. Despite 5 years having passed since the removal of pyrethroids from the control programs, Ae. aegypti remained highly resistant to permethrin and deltamethrin (RR > 10-fold). In addition, following 5 years of chlorpyrifos use, mosquitoes at 15 of 26 sites showed moderate resistance to chlorpyrifos (5- to 10-fold), and the mosquitoes from one site were highly resistant. All sites had low resistance to malathion (< 5-fold). Resistance to bendiocarb was low at 19 sites, moderate at five, and high at two. Frequencies of the V1016I ranged from 0.16-0.71, while C1534 approached fixation at 23 sites (0.8-1). Resistance profiles and kdr allele frequencies varied across Tapachula. The variability was not associated with a spatial pattern at the scale of the sampling.Conclusion/significanceMosquito populations respond to selection pressure at a focal scale in the field. Spatial variation across sites highlights the importance of testing multiple sites within geographical regions.