Comparison of Ground Release and Drone-Mediated Aerial Release of Aedes aegypti Sterile Males in Southern Mexico: Efficacy and Challenges

Diseases transmitted by the mosquito Aedes aegypti, such as dengue, chikungunya and Zika, affect millions of people in tropical and subtropical regions of the world. The sterile insect technique (SIT) is a safe and environmentally benign method of population suppression that could be applied to reduce mosquito-transmitted disease. SIT involves the release of large numbers of sterile male insects that then compete with wild males in mating with females. The females that mate with sterile males do not produce viable offspring. To test this technique within a pilot-scale trial in a village in southern Mexico, we compared two methods for the weekly release of large numbers (approximately 85,000 males/week) of sterile males that were marked with colored powders for later identification. The number of sterile males captured in traps placed in and around houses was higher (average 5.1 males/trap/week) for sterile males released at ground level by technicians walking through the streets of the village. In contrast, traps captured an average of 2.6 males/trap/week when males were released from a small drone aircraft that flew over the village. The males released from the drone may have suffered from chilling, compaction and physical injury during the release procedure. However, the use of the drone resulted in a less aggregated distribution, was markedly quicker, released males over a larger area and required fewer technicians than ground-based releases. Some village residents also reported discomfort from the presence of large numbers of male mosquitoes when released at ground level. Future studies should focus on modifications to the handling and transport of sterile males and the design of drone release containers to avoid injury to sterile mosquitoes and to improve the efficiency of aerial releases for SIT-based suppression of Ae. aegypti in Mexico. Sterile males of Aedes aegypti were released once a week for 8 weeks to evaluate the dispersal efficiency of ground and aerial drone release methods in a rural village of 26 Ha in southern Mexico. Indoor and outdoor BG-Sentinel traps were placed in 13-16 houses distributed throughout the village. The BG traps were activated 48 h after the release of the sterile males and functioned for a 24 h period following each release. Over the 8-week period of simultaneous ground and aerial releases, an average of 85,117 +/- 6457 sterile males/week were released at ground level and 86,724 +/- 6474 sterile males/week were released using an aerial drone. The ground release method resulted in higher numbers of captured males (mean = 5.1 +/- 1.4, range 1.1-15.7 sterile males/trap) compared with the aerial release method (mean = 2.6 +/- 0.8, range 0.5-7.3 sterile males/trap) (p < 0.05). Similarly, the prevalence of traps that captured at least one sterile male was significantly higher for ground release compared to the aerial release method (p < 0.01). The lower numbers of sterile males captured in the aerial release method could be due to mortality or physical injury caused by the chilling process for immobilization, or the compaction of these insects during transport and release. However, aerial releases by a two-person team distributed insects over the entire village in just 20 min, compared to similar to 90 min of work for a five-person team during the ground release method. Ground release also resulted in higher aggregations of males and some villagers reported feeling discomfort from the presence of large numbers of mosquitoes in and around their houses. We conclude that modifications to the handling and transport of sterile males and the design of containers used to store males are required to avoid injury and to improve the efficiency of aerial releases for area-wide SIT-based population suppression programs targeted at mosquito vectors of human disease.