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. Author summary Wild-type female Ae. aegypti mating with released males carrying the maternally inherited bacteria Wolbachia produce infertile eggs, leading to important reductions in mosquito population size. We present results from pilot open-field mass-releases of Ae. aegypti males infected with the Wolbachia strain wAlbB (termed incompatible insect technique, IIT) and irradiated to prevent accidental female mosquito colonization (termed sterile insect technique, SIT). Our IIT-SIT approach was implemented by the Mexican Ministry of Health within an Integrated Vector Management (IVM) plan to suppress natural populations of Ae. aegypti. Approximately 1,270,000 lab-produced wAlbB-infected Ae. aegypti males were released in a 50-ha. town of Yucatan over a period of 24 weeks. Throughout the suppression phase, we observed significant reductions in egg hatching, outdoor and indoor female Ae. aegypti densities in the release town compared to a similar town used as control. The largest effect was on the number of indoor Ae. aegypti females per house (Prokopack collections) which reached a 90% efficacy. Our study, the first report of an open-field pilot-study with mass-releases of sterile Ae. aegypti males produced with IIT-SIT in Mexico and Latin-America, confirms findings from other settings showing important reductions in entomological indices due to inundative incompatible male releases.