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

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.

Strategies to Mitigate Establishment under the Wolbachia Incompatible Insect Technique

“…The suppression approach (S2) using the first strain at FRERs of 10 −3 and 10 −9 resulted in an 82.4% (95% UI: 80.0-85.0%) and 82.5% (95% UI: 79.7-85.4%) decline in the wild-type female population, respectively (Figure 2C,D), relative to the baseline (S1) equilibrium wild-type population. These results confirm the levels of suppression achieved on the wild type female mosquito population from ecological experiments [43,44].…”

New self-sexing Aedes aegypti strain eliminates barriers to scalable and sustainable vector control for governments and communities in dengue-prone environments

“…Red-eye genetic sexing strains have also been developed for Aedes aegypti , but these similarly rely on expensive automated sex-sorting for efficient production ( Koskinioti et al, 2021 ). For some, imperfect manual sex-sorting leads to the need for additional irradiation sterilisation steps ( Zheng et al, 2019 ; Martín-Park et al, 2022 ), or RNAi-based sterilization ( De Castro Poncio et al, 2021 ) which also add cost and complexity. A further operational restriction is the short shelf-life of adult male mosquitoes (sometimes requiring release within as little as 24 h after production ( Crawford et al, 2020 )) that has limited the locations in which these tools can be used, as they either require local production facilities, or fast and efficient shipping of live mosquitoes in climate-controlled conditions to release sites.…”

“…These strategies employ male Aedes aegypti that when mated with wild females render some or all the offspring unviable. The sterile insect technique (SIT), involving irradiation of mosquitoes to induce sterility and physical sex-sorting to enable male-only releases, has historically not been successful for Aedes aegypti ( Morlan et al, 1962 ; Ogah and Juma, 1977 ), though some recent successes in small-scale trials in Mexico (involving a combination of SIT and Wolbachia -infected males) and Cuba indicate a renewed interest in SIT for Aedes aegypti ( Gato et al, 2021 ; Martín-Park et al, 2022 ).…”

Current Status of Mosquito Handling, Transporting and Releasing in Frame of the Sterile Insect Technique

“…aegypti control) and Mexico (IIT–SIT for Ae. aegypti control) in a mosquito control project [ 27 , 50 , 52 ].…”