Incompatible Aedes aegypti male releases as an intervention to reduce mosquito population : A field trial in Puerto Rico

Mosquito-transmitted viruses such as dengue are a global and growing
public health challenge.  Without widely available vaccines,
mosquito control is the primary tool for fighting the spread of these
viruses. New mosquito control technologies are needed to complement
existing methods.  A field trial was conducted in collaboration
with the Communities Organized to Prevent Arboviruses project in Ponce,
Puerto Rico, to measure entomological and epidemiological effects of
reducing Aedes aegypti populations using Wolbachia incompatible insect
technique.  We packed and shipped Wolbachia-males from California
and released them into 19 treatment clusters from September 2020 to
December 2020. The preliminary evaluation revealed sub-optimal
Wolbachia-male densities and impact on the wild-type population. In 2021,
we shifted to a phased release strategy starting in four clusters,
reducing the mosquito population by 51% (CI 31–71%).  We describe
the investigation into male quality and other factors that may have
limited the impact of Wolbachia-male releases.  Laboratory assays
showed a small but significant impact of the packing and shipping process
on male fitness. However, mark-release-recapture assessments suggest that
male daily survival rates in the field may have been significantly
impacted.  We compared induced-sterility levels and suppression
of the wild population and found patterns consistent with mosquito
population compensation in response to our intervention.
 Analysis of epidemiological impact was not possible due to very
low viral transmission rates during the intervention period.  Our
entomological impact data provide evidence that Wolbachia
incompatible-male releases reduced Ae. aegypti populations, although
efficacy will be maximized when releases are part of an integrated control
program.  With  improvement of shipping vessels and
shipped male fitness, packing and shipping male mosquitoes could provide a
key solution for expanding access to this technology in Puerto Rico. Our
project underscores the challenges involved in large and complex field
assessments of the effectiveness of novel vector control methods.