Aerial larviciding across Grand Cayman began on 11 September 2026, with the Mosquito Research and Control Unit (MRCU) saying the operation would start in West Bay, move east and take about a week, weather permitting.

Residents will see the unit's aircraft flying low during daylight hours and passing repeatedly over the same ground. "These repeated passes are necessary to ensure effective and thorough coverage of mosquito breeding areas," MRCU said in a release issued on 11 September 2026. The unit said its pilots "are specially trained to carry out this type of work" and that low altitude was needed to place the larvicide accurately.

The treatment will not relieve the biting that has followed recent heavy rain. In an e-mailed response to questions from The Caymanian Journal (TCJ) on 11 September 2026, MRCU said: "This larviciding treatment will not affect mosquitoes that have already emerged as adults. Instead, it kills larvae within the treated wetland areas and helps prevent them from developing and emerging as additional biting adults." Adult mosquito control operations would continue "where surveillance data indicates they are required", the unit said. Aerial adulticiding is flown in the evenings, starting about 15 minutes after sunset.

What is being dropped, and where

The product is Natular G30, a granular larvicide whose active ingredient is spinosad, made by Clarke Mosquito Control Products, Inc. of Roselle, Illinois, and registered with the U.S. Environmental Protection Agency under registration number 8329-83. The label, published on the MRCU products page, states that the granule contains 2.5% spinosad and "releases effective levels of spinosad for up to 30 days under typical environmental conditions". Spinosad is derived from the fermentation of a naturally occurring soil bacterium. The label approves fixed-wing aircraft and helicopters fitted with granular spreaders at rates of five to 20 pounds per acre.

MRCU told TCJ it is applying the product at 8 pounds per acre. The primary target is Aedes taeniorhynchus, the black salt marsh mosquito, which the unit called "Cayman's primary nuisance mosquito" and which MRCU has said in earlier statements "is not known to transmit human disease locally", though it can carry heartworm to dogs and cats. The operation is aimed at wetland breeding areas rather than residential districts: "The aerial larviciding operation is targeting wetland breeding areas where this species develops," the unit said, adding that it uses surveillance data, rainfall and tidal conditions, trap counts and mapping to decide where to treat.

The unit would not give an acreage. "The exact acreage to be treated cannot be determined in advance," it said, because the extent depends on rainfall, tides and trap counts gathered as the operation goes on.

The label carries the U.S. signal word "CAUTION" and states "Harmful if swallowed" and "Causes moderate eye irritation". Under environmental hazards it states: "This product is toxic to aquatic organisms. Non-target aquatic invertebrates may be killed in waters where this pesticide is used." It also prohibits application to "natural or artificial containers of water intended for consumption by people, animals, or livestock". Asked how it manages those conditions when applying granules from the air over an inhabited island, MRCU said: "MRCU does not apply Natular G30 to cisterns, ornamental ponds or other sites that are not approved for treatment under the product label." It said the label lists freshwater and brackish swamps and marshes, mangroves and other coastal areas as approved habitats, and that "environmental precautions relating to aquatic organisms" are taken into account when treatment areas are identified.

On 28 September 2025 MRCU described the growth regulator it was then applying by air as posing "no risk to people, pets, beneficial insects, or the environment". Asked whether it made the same statement about Natular G30, the unit did not repeat the wording. It said: "MRCU is confident in its safe and effective use when applied in accordance with the approved product label."

The season so far

MRCU's own figures show why the operation is wide. In a statement dated 4 August 2026, the unit said preliminary surveillance data for 2026 showed a year-to-date average of about 40 mosquitoes per trap night, against about 29 in 2025 and about 57 in 2023. A release of 25 June 2026 put the season's peak at 9,309 mosquitoes collected on 18 June; a second wave in July produced a daily total of more than 5,000. The black salt marsh mosquito lays eggs in wetland soil that lie dormant until tides or rain flood them, which is why MRCU said in July that yard clean-ups would not prevent its emergences, though they help against other species.

MRCU said in its 11 September release that recent rainfall had created "additional opportunities for mosquitoes to breed around homes and properties" and asked residents to walk their property at least once a week and empty, turn over or dispose of anything holding water.

Aircraft, drones and money

MRCU has carried out this kind of operation before. On 26 November 2025 it announced island-wide aerial larviciding of Grand Cayman expected to take two weeks, followed by the Sister Islands in early to mid-December. On 26 February 2026 it treated Barkers, Camana Bay, Old Prospect Point, Salt Creek and the area around the airport, and on 17 and 20 April 2026 the West Bay peninsula.

Both of the unit's aircraft are flying. On 10 June 2026 MRCU said it was "operating with one aircraft temporarily out of service". Asked about that aircraft, the unit told TCJ it "returned to service on 11 June 2026 following the necessary checks and clearance" and that both aircraft had been operational since. One is configured for granular larviciding and is flying this operation; the other is set up for adulticiding and liquid larviciding.

The unit's application drones are still out. On 4 August 2026 MRCU said it "currently has no application drones available for mosquito control". It told TCJ it expects to restore that capability "before the end of the year", and that its DJI Mavic 3E drones, used for surveying and mapping, remain in service.

MRCU was flying with a single aircraft for a period last year. On 19 November 2025 the Minister for Health, Environment and Sustainability, Katherine Ebanks-Wilks MP, told Parliament's Finance Committee that MRCU's programme "relies on a fleet of two aircraft that have exceeded their optimal service life and the required maintenance is costly". Presenting what she called a Key Capital Project of the 2026-2027 budget, she said the Government was "planning to invest CI$1,800,000 in the procurement of a replacement aircraft". Asked by Roy McTaggart MP, the member for George Town East, whether the unit had two aircraft, she said: "The second aircraft is down because the engine had issues that needed to be repaired, so we're down one aircraft and now we're seeking to purchase a new one." Roy McTaggart MP replied that the aircraft were "quite old and worn out" and that "we don't need one, we need two". No announcement of an order for a replacement aircraft appears among MRCU's published releases since that date.

Separately from the aircraft, the same sitting approved the unit's operating appropriation, Mosquito Control Services, at CI$10,155,000 for 2026 and CI$10,354,000 for 2027, according to the Official Finance Committee Report for that day.

What this operation will cost is not yet known. MRCU said the quantity of Natular G30 and the flight hours "cannot be finalised at this stage" because both depend on the acreage finally treated, and that the product cost and operational cost "can be determined once the extent of the treatment is known".

MRCU expects to begin the Sister Islands phase "immediately following completion of the Grand Cayman operation, currently anticipated at approximately 20 September, weather and operational conditions permitting". It gave no estimate of when residents should expect fewer mosquitoes as a result of this treatment, saying only that the granules stay active for up to 30 days and that adult control would continue where the data called for it.