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. 2022 Apr 26;16(4):e0010324.
doi: 10.1371/journal.pntd.0010324. eCollection 2022 Apr.

Pilot trial using mass field-releases of sterile males produced with the incompatible and sterile insect techniques as part of integrated Aedes aegypti control in Mexico

Abdiel Martín-Park  1 , Azael Che-Mendoza  1 , Yamili Contreras-Perera  1 , Silvia Pérez-Carrillo  1 , Henry Puerta-Guardo  1 , Josué Villegas-Chim  1 , Guillermo Guillermo-May  1 , Anuar Medina-Barreiro  1 , Hugo Delfín-González  1 , Rosa Méndez-Vales  2 , Santos Vázquez-Narvaez  2 , Jorge Palacio-Vargas  2 , Fabián Correa-Morales  3 , Guadalupe Ayora-Talavera  4 , Norma Pavía-Ruz  4 , Xiao Liang  5 , Ping Fu  5   6 , Dongjing Zhang  7 , Xiaohua Wang  8 , María Eugenia Toledo-Romaní  9 , Zhiyong Xi  5   7 , Gonzalo Vázquez-Prokopec  10 , Pablo Manrique-Saide  1
Affiliations

Pilot trial using mass field-releases of sterile males produced with the incompatible and sterile insect techniques as part of integrated Aedes aegypti control in Mexico

Abdiel Martín-Park et al. PLoS Negl Trop Dis. .

Abstract

Background: The combination of Wolbachia-based incompatible insect technique (IIT) and radiation-based sterile insect technique (SIT) can be used for population suppression of Aedes aegypti. Our main objective was to evaluate whether open-field mass-releases of wAlbB-infected Ae. aegypti males, as part of an Integrated Vector Management (IVM) plan led by the Mexican Ministry of Health, could suppress natural populations of Ae. aegypti in urbanized settings in south Mexico.

Methodology/principal findings: We implemented a controlled before-and-after quasi-experimental study in two suburban localities of Yucatan (Mexico): San Pedro Chimay (SPC), which received IIT-SIT, and San Antonio Tahdzibichén used as control. Release of wAlbB Ae. aegypti males at SPC extended for 6 months (July-December 2019), covering the period of higher Ae. aegypti abundance. Entomological indicators included egg hatching rates and outdoor/indoor adult females collected at the release and control sites. Approximately 1,270,000 lab-produced wAlbB-infected Ae. aegypti males were released in the 50-ha treatment area (2,000 wAlbB Ae. aegypti males per hectare twice a week in two different release days, totaling 200,000 male mosquitoes per week). The efficacy of IIT-SIT in suppressing indoor female Ae. aegypti density (quantified from a generalized linear mixed model showing a statistically significant reduction in treatment versus control areas) was 90.9% a month after initiation of the suppression phase, 47.7% two months after (when number of released males was reduced in 50% to match local abundance), 61.4% four months after (when initial number of released males was re-established), 88.4% five months after and 89.4% at six months after the initiation of the suppression phase. A proportional, but lower, reduction in outdoor female Ae. aegypti was also quantified (range, 50.0-75.2% suppression).

Conclusions/significance: Our study, the first open-field pilot implementation of Wolbachia IIT-SIT in Mexico and Latin-America, confirms that inundative male releases can significantly reduce natural populations of Ae. aegypti. More importantly, we present successful pilot results of the integration of Wolbachia IIT-SIT within a IVM plan implemented by Ministry of Health personnel.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1
A) Field sites located in the periphery of the city of Merida, southeast of Mexico; San Pedro Chimay (release site) shown in orange and Tahdzibichén (control site) in blue; B) Distribution of one-hectare areas within localities, where sentinel areas for entomological surveillance were located and releases were performed (only at San Pedro Chimay); C) Proposed an Integrated Vector Management plan combining ‘traditional Aedes control’ and the release of X-ray irradiated male Ae. aegypti carrying Wolbachia for population suppression structured in three phases: Preparation: with community sensitization and engagement, and baseline entomological studies; Attack: initial traditional vector control; and Suppression phase: with inundative releases during peak of mosquito abundance; D) Sterile male mosquitoes released in a backyard by personnel of the MoH; E) "Uts koxol” (“good mosquitoes” in Mayan language). Maps were produced using QGIS based on public geographic data obtained from OpenStreetMap (www.openstreetmap.org).
Fig 2
Fig 2
A) Laboratory of Biological Control for Aedes aegypti (LCB-UADY). B) Schematic representation of the main processes at LCB-UADY to produce wAlbB Ae. aegypti mosquitoes with the sterile insect technique using radiation (IIT-SIT). As part of the Q.C., we optimized a PCR assay to detect the presence of Wolbachia infection in every generation of adult mosquitoes under mass-rearing system as well as before every release.
Fig 3
Fig 3. Entomological indicators of population suppression between release (San Pedro Chimay = red line) and control (Tahdzibichén = black line) sites.
A) Mean hatching rate (SD) per week, B) Mean No. of females captured with BG traps (SD), C) Mean No. of indoor females captured with Prokopack aspirators, D) Average temperature and precipitation during the study period. Grey-shaded regions indicate release periods. The dashes in the X-axis represent the weeks of the year.
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Publication types

Grants and funding

This research was funded by grant YUC-2017-03-01-556 awarded to PMS by the Fondo Mixto Consejo Nacional de Ciencia y Tecnología (CONACYT) (México)-Gobierno del Estado de Yucatán and grant AID-OAA-F-16-00082 awarded to ZX by the U.S. Agency for International Development (USAID). AM-P is supported by the Catedras-CONACYT program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.