The Mosquito Research and Control Unit (MRCU) is advising residents to expect another noticeable increase in mosquito activity across Grand Cayman from the beginning of next week. This will be the second noticeable increase during the current mosquito and rainy season and is consistent with the seasonal conditions typically experienced at this time of year.
The expected increase is being driven by a combination of seasonal tidal flooding and recent rainfall. Higher tides have flooded wetland areas, while rainfall on already saturated ground has created additional standing-water sites in low-lying areas, roadside drains and other locations. MRCU field teams have found mosquito larvae at numerous sites across Grand Cayman and are treating breeding areas based on surveillance data and field inspections.
Why Flooding Leads to More Mosquitoes
Black salt marsh mosquito eggs can remain dormant in wetland soil until water levels rise. Once the wetlands are flooded, the eggs hatch and the larvae develop in the shallow water. When large areas flood at the same time, a widespread emergence of adult mosquitoes can follow several days later.
The main species expected to emerge in increased numbers is Aedes taeniorhynchus, commonly known as the black salt marsh mosquito. It is an active biter, can fly several miles from wetlands and is generally most active around sunrise and sunset. Daytime biting will likely also occur, particularly in shaded areas around trees, shrubs and other vegetation.
Black salt marsh mosquitoes do not transmit diseases to humans and are not considered a public-health threat to people. However, they can transmit heartworm to dogs and cats. Pet owners should ensure their animals remain up to date with heartworm prevention.
MRCU Increasing Control Operations
MRCU is increasing both larval and adult mosquito control operations. Aircraft missions are planned for the evening, shortly after sunset, when weather conditions allow. Truck foggers will support operations in targeted areas, while ground teams will treat known breeding sites with larvicides to prevent larvae from developing into adult mosquitoes.
Operations are directed by surveillance data, larval surveys, field inspections, mosquito activity and weather conditions. Strong winds, rain or other unsuitable conditions may delay aircraft or truck fogging operations. With large numbers of mosquitoes expected to emerge from extensive wetland areas over a short period, several days of sustained control operations will be required before residents notice a reduction in activity.
Even with extensive control efforts, biting should be expected during a widespread seasonal emergence. The public may not see every operation taking place because treatments are targeted to the locations and times where they are expected to have the greatest effect.
How Residents Can Reduce Mosquito Bites
Removing standing water around homes remains important for controlling other mosquito species. However, it will not prevent this particular emergence because black salt marsh mosquitoes breed in flooded wetlands rather than residential yards.
MRCU teams will continue monitoring mosquito activity across Grand Cayman and adjusting operations based on the information collected. Residents are encouraged to follow MRCU’s social media platforms for updates on mosquito activity and ongoing control operations.