Insecticide susceptibility status of Anopheles albimanus populations in historical malaria foci in Quintana Roo, Mexico.

BACKGROUND: Mexico has experienced a significant reduction in malaria cases over the past two decades. Certification of localities as malaria-free areas (MFAs) has been proposed as a steppingstone before elimination is achieved throughout the country. The Mexican state of Quintana Roo is a candidate for MFA certification. Monitoring the status of insecticide susceptibility of major vectors is crucial for MFA certification. This study describes the susceptibility status of Anopheles albimanus, main malaria vector, from historically important malaria foci in Quintana Roo, using both phenotypic and genotypic approaches. METHODS: Adult mosquito collections were carried out at three localities: Palmar (Municipality of Othon P. Blanco), Buenavista (Bacalar) and Puerto Morelos (Puerto Morelos). Outdoor human-landing catches were performed by pairs of trained staff from 18:00 to 22:00 during 3-night periods at each locality during the rainy season of 2022. Wild-caught female mosquitoes were exposed to diagnostic doses of deltamethrin, permethrin, malathion, pirimiphos-methyl or bendiocarb using CDC bottle bioassays. Mortality was registered at the diagnostic time and recovery was assessed 24 h after exposure. Molecular analyses targeting the Voltage-Gated Sodium Channel (vgsc) gene and acetylcholinesterase (ace-1) gene were used to screen for target site polymorphisms. An SNP analysis was carried out to identify mutations at position 995 in the vgsc gene and at position 280 in the ace-1 gene. RESULTS: A total of 2828 anophelines were collected. The main species identified were Anopheles albimanus (82%) and Anopheles vestitipennis (16%). Mortalities in the CDC bottle bioassay ranged from 99% to 100% for all the insecticides and mosquito species. Sequence analysis was performed on 35 An. albimanus across the three localities; of those, 25 were analysed for vgsc and 10 for ace-1 mutations. All individuals showed wild type alleles. CONCLUSION: The results demonstrated that An. albimanus populations from historical malaria foci in Quintana Roo are susceptible to the main insecticides used by the Ministry of Health.

Mosquito species (Diptera: culicidae) collected after tropical storm cristobal in Merida, Yucatan, South-east Mexico.

After the tropical storm Cristobal, we performed special adult entomological collections in the peri-domicile of 35 houses from 25 neighborhoods of Mérida, Yucatan, Mexico in response to complaints from the community about an increased nuisance due to an abundance of mosquitoes. A total of 1,275 specimens from four genera and 13 species were collected: Aedes taeniorhynchus (92%), Culex quinquefasciatus (72%), Aedes aegypti (72%), Psorophora mexicana (36%), Psorophora cyanescens (32%), Aedes scapularis (24%), Culex nigripalpus (24%), Aedes albopictus (8%), Psorophora ferox (4%), Haemagogus equinus (4%), Aedes trivittatus (4%), Culex coronator (4%), Culex iolambdis (4%). From these collections, the increased mosquito nuisance was mainly the result of invasive species such as Aedes taeniorhynchus and Psorophora. City wide, vehicle mounted ULV spraying was performed by the MoH and the municipality of Merida to control adult mosquito populations. We report Culex iolambdis for the first time in Merida and Psorophora mexicana for the state of Yucatan.

Targeted indoor residual insecticide applications shift Aedes aegypti age structure and arbovirus transmission potential.

While residual insecticide applications have the potential to decrease pathogen transmission by reducing the density of vectors and shifting the age structure of the adult mosquito population towards younger stages of development, this double entomological impact has not been documented for Aedes aegypti. Aedes collected from households enrolled in a cluster-randomized trial evaluating the epidemiological impact of targeted indoor residual spraying (TIRS) in Merida, Mexico, were dissected and their age structure characterized by the Polovodova combined with Christopher's ovariole growth methods. In total, 813 females were dissected to characterize age structure at 1, 3, 6, and 9 months post-TIRS. Significant differences in the proportion of nulliparous Ae. aegypti females between the treatment groups was found at one-month post-TIRS (control: 35% vs. intervention: 59%), three months (20% vs. 49%) but not at six or nine months post-TIRS. TIRS significantly shiftted Ae. aegypti age structure towards younger stages and led to a non-linear reduction in survivorship compared to the control arm. Reduced survivorship also reduced the number of arbovirus transmitting females (those who survived the extrinsic incubation period). Our findings provide strong evidence of the full entomological impact of TIRS, with important implications for quantifying the epidemiological impact of vector control methods.

Phlebotomine sand flies (Diptera: Psychodidae) from an emergent focus of localized cutaneous leishmaniasis in Yucatan, Southeast Mexico.

Localized cutaneous leishmaniasis (LCL) is endemic in the Yucatan Peninsula, with historical and contemporary records mainly in the states of Campeche and Quintana Roo. Recently, we reported autochthonous LCL cases and 27.6% of asymptomatic infection in the municipality of Tinum, Yucatan, where no studies of Phlebotominae (Diptera: Psychodidae) sand flies have been carried out. In this work, from November, 2019 to February, 2020, we conducted a field study in three areas of Tinum to document, for the first time, the species of Phlebotominae in areas with records of human leishmaniasis transmission. In order of abundance, the species identified were Pifanomyia serrana, Psathyromyia shannoni, Psathyromyia cratifer, Lutzomyia cruciata, Bichromomyia olmeca olmeca, and Dampfomyia deleoni. Most of the sand flies were captured in a Shannon trap where 77.8% of collected specimens were females. The distribution of sand fly species showed some degree of heterogeneity among sites, and the highest species richness was registered in a site located in Xcalakoop. We also discuss the medical importance of Lu. cruciata, Ps. shannoni, and Pi. serrana as potential vectors of causal agents of LCL in this area.

Insecticide Susceptibility Tests of Aedes taeniorhynchus in Yucatan, Mexico.

We report results of susceptibility tests for Aedes taeniorhynchus from 2 localities of Yucatan State, Mexico, to different insecticides. The Centers for Disease Control and Prevention bottle bioassays were performed using the active ingredients of 3 pyrethroids, 2 organophosphates, and 1 carbamate: permethrin (15 µg/ml), deltamethrin (10 µg/ml), alpha-cypermethrin (10 µg/ml), malathion (50 µg/ml), chlorpyrifos (85 µg/ml), and bendiocarb (12.5 µg/ml). The mortality recorded at the diagnostic time of exposure (30 min) was 100% with all insecticides evaluated and for both populations. These results suggest complete susceptibility to the 3 chemical groups generally used for urban Ae. aegypti mosquito control.

Olbiogaster Osten Sacken (Diptera: Anisopodidae) from Mexico, with the description of three new species.

Three new species of the genus Olbiogaster Osten Sacken-Olbiogaster halffteri sp. nov., Olbiogaster nuxco sp. nov. and Olbiogaster puuc sp. nov.-are described and illustrated from Mexico, based on adult males and females collected in the states of Guerrero, Puebla and Yucatan. Comments for the species known from Mexico and key are provided.

A Survey of the Mosquito Species in Maxcanu, Yucatan, Mexico.

A survey was carried out to identify the mosquitoes inhabiting human premises in the rural locality of Maxcanú, Yucatán, Mexico. Using the Centers for Disease Control and Prevention backpack aspirators, simple random sampling was carried out inside of 101 homes during the November 2013 rainy season. A total of 1,492 specimens were collected. Three subfamilies (Anophelinae, Culicinae, and Toxorhynchitinae) and 5 species were identified: Anopheles albimanus, Aedes aegypti, Culex interrogator, Limatus durhamii, and Toxorhynchites theobaldi. The most abundant species was Cx. interrogator (74%) followed by Ae. aegypti (25%). The Chao 1 and Bootstrap species richness estimator indicated that it was possible to collect 90% of the expected species. This is the 1st time that the presence of An. albimanus, Cx. interrogator, Li. durhamii, and Tx. theobaldi has been recorded in Maxcanú.