The Mosquito Research and Control Unit uses a number of insecticides with chemicals known to be toxic to bees, aquatic life and, in some cases, humans, according to documents received through a Cayman Compass freedom of information request. 

The MRCU conducted at least 1,900 operations using these chemical products to combat Cayman’s mosquitos since January 2019. Those operations incorporated more than 20 different products, including 10 chemical pesticides and a soil-dwelling bacteria.

Nearly US$4 million was spent on pesticides over the same period, according to MRCU data.

Jim McNelly, director of MRCU, spoke to the Cayman Compass about the variety of chemicals used in mosquito control operations and why he suggests ducking inside if the MRCU plane passes overhead.

Cayman Compass: MRCU uses a long list of chemical products for mosquito control. Why so many?

Jim McNelly: The reason we used the different products… in part is related to resistance management. What we don’t want to do is use the same product over and over and over for years at a time and potentially create a resistance problem in one or more of our mosquito species.

CC: What do you mean by resistance?

JM: The ones that are genetically predisposed to being resistant to that particular active ingredient ultimately begin to reproduce the resistance gene, [it] spreads through the population and the next thing you know, you have a problem.

CC: Many products come with warnings about risks to bees and aquatic life. How do you mitigate those risks?

JM: MRCU will begin operations to kill adult mosquitoes 20 minutes to half hour after sunset. Most of your bees are then inactive. They’re back at the hive … Basically you’re using timing to avoid, to mitigate the risks to bees.

CC: What about the risk to aquatic life?

JM: As long as we have our planes properly calibrated and characterised and are going out at the label rates … we’re minimising the impacts to any of the bodies of water that we might fly over. … We’re using these products at a dosage that if you look at the scientific literature, the body of work that supports the use of these formulations, [it] minimises the risk to everything that you’ve mentioned in your warning: aquatic organisms, fish, crabs.

CC: Is any kind of testing done on mangroves or other bodies of water to measure chemical presence?

JM: Not presently. On Grand Cayman, I believe, well before I got here, the unit was either doing that voluntarily or was tasked with that responsibility. But we haven’t done it for years.

CC: Why not?

JM: As long as we’re doing things correctly, we’re confident that there aren’t impacts to bodies of water. … We always say that the people that work in mosquito control are also the people who live here on this island. The last thing people in mosquito control want to do is impact the environment.

CC: If I’m outside on a patio when the mosquito plane passes overhead, should I worry about being sprayed?

JM: There’s the potential, yes, to be sprayed. And we always tell people that if you see the truck, if you see the plane, to do your best to avoid being outside for the next 15, 20 minutes, because that’s about as long as that spray is going to be in the air.

CC: So, if I’m on a restaurant patio, should I ask the waiter to move me inside?

JM: I don’t think it’s a bad idea if that’s an option.

We have flight plans that are set to avoid, for instance, the Camana Bay area when that area is active with all of the outdoor seating. So we fly west of Camana Bay and avoid flying east to avoid, again, all these folks that are potentially outside. We’ll do a more prescriptive application in that area with trucks, again, to avoid most of those outdoor people. When the guys are spraying with the trucks, if they see people on the road, walking, jogging, walking the dog, they’re supposed to shut off the machines to avoid spraying people.

Insecticides and larvicides used in mosquito-control operations:

Agua Reslin
Warnings: Extremely toxic to fish and aquatic invertebrates, highly toxic to bees, runoff hazardous to aquatic organisms
Frequency: 422 times

VectoBac GS (Granule)
Hazards/Warnings: Irritation to eyes, risk of allergic sensitisation after repeated exposure to high concentrations
Frequency: 195 times

MosquitoMist Two
Warnings: Toxic to fish, aquatic invertebrates, small mammals and birds, highly toxic to bees, runoff hazardous to fish and aquatic invertebrates
Frequency: 167 times

VectoBac WDG (water-dispersible granule)
Frequency: 144 times

Deltagard
Warnings: Extremely toxic to fresh water and estuarine fish and invertebrates, runoff may be hazardous to fish and aquatic invertebrates, highly toxic to bees
Frequency: 117 times

Fyfanon ULV
Warnings: Highly toxic to bees, toxic to fish, aquatic invertebrates, and aquatic life stages of amphibians
Frequency: 55 times (Malathion, the active ingredient in Fyfanon ULV also listed 141 times)

Summit (Mosquito Bits)
Warnings: Extremely toxic to fish
Frequency: 55 times

Altosid XR-G
Warnings: Carcinogenicity category 1A (may cause cancer), causes damage to organs through prolonged exposure
Frequency: 50 times

Natular G30
Warnings: Toxic to aquatic invertebrates, runoff may be hazardous to aquatic organisms, highly toxic to bees
Frequency: 42 times

Agua Pursuit
Warnings: Extremely toxic to fish and aquatic invertebrates, highly toxic to bees, runoff hazardous to aquatic organisms
Frequency: 41 times

Merus
Warnings: Toxic to aquatic organisms, including fish and aquatic invertebrates, runoff off may be hazardous to fish and aquatic invertebrates, highly toxic to bees
Frequency: 27 times

Censor
Warnings: Toxic to aquatic invertebrates, runoff may be hazardous to aquatic organisms, highly toxic to bees
Frequency: 23 times

Natular SC
Warnings: Toxic to aquatic invertebrates, runoff may be hazardous to aquatic organisms, highly toxic to bees and pollinating insects
Frequency: 21 times

VectoBac FG (Fine Granule)
Frequency: 5 times

Natular
Warnings: Toxic to aquatic invertebrates, runoff may be hazardous to aquatic organisms, highly toxic to bees
Frequency: 2 times

Other mosquito-control products used in unspecified capacity:
565 Plus XLO
Warnings: Toxic to aquatic organisms, including fish and invertebrates, runoff hazardous to aquatic life, highly toxic to bees

Abate 4E
Warnings: Toxic to aquatic organisms such as stoneflies, water fleas and shrimp, may affect population diversity

Altosid Pro-G

Aquabac 200 G/CG Granule

Top of Descent

Note: Uses include both ground and air operations between January 2019 and September 2020.

What’s found in Cayman’s mosquito sprays?

Permethrin – Insecticide found in medication to treat scabies and lice.
Chlorpyrifos – Pesticide attacks the nervous system of pests and insects. Considered moderately hazardous to humans by the World Health Organization.
Pyrethrins – Insecticide targets the nervous system of insects. This class of organic compound is biodegradable and toxicity to humans is considered low.
Malathion – Insecticide approved to treat head lice. Considered low toxicity to humans.
Methoprene – Hormone doesn’t kill insects but inhibits their life cycle and prevents maturity, reproduction.
Spinosad – Insecticide that can be used to treat fleas and head lice.
Deltamethrin – Compound belonging to a group of pesticides that are highly toxic to aquatic life. While it is considered generally safe around humans, it is neurotoxic and should be avoided.
Bacillus thuringiensis, subspecies israelensis – Bacteria used for biological control of mosquito larvae.
Temephos – Larvicide used to treat waters infested with insects like mosquitos.
Lambda-cyhalothrin – Insecticide that is highly toxic to bees and fish.
Phenothrin – Synthetic compound used to kill fleas and head lice. Has been linked to adverse effects such as hair loss and deaths of cats.
n-Octyl Bicycloheptene Dicarboximide – Ingredient does not have inherent pesticide qualities but instead helps enhance the potency of pyrethroid ingredients.
Piperonyl butoxide – Ingredient has no pesticide qualities but instead helps enhance the potency of certain ingredients.

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2 COMMENTS

  1. Omg this is the worst article I’ve ever read about the island. It’s full of naïveté. Y’all have no idea what damage you’re doing. Who recommended getting rid of all the lizards? Why do you know so little about your own ecosystem? It’s shocking. These chemicals don’t just disappear after a few minutes.

  2. We don’t need any of this poison.
    Is it even working?
    The mosquitoes by my house are horrible. But I would rather deal with the mosquitoes rather than expose my family to harmful chemicals that will shorten their our lives. Let us stop spraying for a year, and see if it makes any difference.