The battle towards mosquitoes: breaking down the chemical compounds utilized by the MRCU


The Mosquito Research and Control Unit uses a range of insecticides with chemicals known to be toxic to bees, aquatic life, and in some cases, humans. This is evident from documents received through a Freedom of Information request from Cayman Compass.

The MRCU has performed at least 1,900 operations with these chemical products to control Cayman mosquitoes since January 2019. These operations involved more than 20 different products, including 10 chemical pesticides and one soil-dwelling bacterium.

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

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

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

Jim McNelly: Part of the reason we used the different products is related to resistance management. What we don’t want is to keep using the same product over and over again for years and possibly creating a resistance problem in one or more of our mosquito species.

CC: What do you mean by resistance?

JM: Those who are genetically predisposed to be resistant to that particular drug will eventually begin to reproduce the resistance gene. [it] is spreading in the population and next you have a problem.

CC: Many products contain warnings about risks to bees and aquatic life. How do you mitigate these risks?

JM: The MRCU will begin killing adult mosquitoes 20 minutes to half an hour after sunset. Most of your bees are then inactive. You’re back in the hive … Basically, you are using timing to avoid and reduce the risks to bees.

CC: What about the risk to aquatic life?

JM: As long as we have properly calibrated and characterized our planes and are running out with labeling rates … we are minimizing the impact on the bodies of water we might fly over. … We use these products in a dosage that, if you look at the scientific literature, is the work that supports the use of these formulations. [it] minimizes the risk of everything you mentioned in your warning: aquatic organisms, fish, crabs.

CC: Are tests carried out on mangroves or other bodies of water to measure the presence of chemicals?

JM: Currently not. I believe the unit on Grand Cayman either volunteered or was given this responsibility long before I arrived. But we haven’t done it in years.

CC: Why not?

JM: As long as we do things right, we are confident that water will have no impact. … We always say that the people who work in mosquito control are also the people who live here on this island. The last thing people want to do in mosquito control is polluting the environment.

CC: If I’m outside on a deck with the mosquito plane flying overhead, should I worry about getting sprayed?

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

CC: If I’m on a restaurant terrace, should I ask the waiter to pull me in?

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

We have flight schedules designed to avoid, for example, Camana Bay when it is active with all outdoor seating. So we fly west of Camana Bay and avoid flying east to avoid all of these people who may be outside. We’ll be doing a more precise trucking application in this area again to avoid most of these people in the open. When the guys spray with the trucks, when they see people on the street, when they go, jog, walk the dog, they should turn off the machines to avoid people spraying.

Insecticides and larvicides to control mosquitoes:

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

VectoBac GS (granules)
Hazards / warning notes: Eye irritation, risk of allergic sensitization 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 dangerous to fish and aquatic invertebrates
Frequency: 167 times

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

Warnings: Extremely toxic to freshwater, estuarine fish and invertebrates. Runoff can be dangerous to fish and aquatic invertebrates and 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 bites)
Warnings: Very toxic to fish
Frequency: 55 times

Altoside XR-G
Warnings: Carcinogenicity category 1A (can cause cancer) leads to organ damage after prolonged exposure
Frequency: 50 times

Natular G30
Warnings: Toxic to aquatic invertebrates, runoff can be dangerous to aquatic organisms and highly toxic to bees
Frequency: 42 times

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

Warnings: Toxic to aquatic organisms including fish and aquatic invertebrates. Drainage can be dangerous for fish and aquatic invertebrates and highly toxic for bees
Frequency: 27 times

Warnings: Toxic to aquatic invertebrates, runoff can be dangerous to aquatic organisms and highly toxic to bees
Frequency: 23 times

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

VectoBac FG (fine granules)
Frequency: 5 times

Warnings: Toxic to aquatic invertebrates, runoff can be dangerous to aquatic organisms and 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 dangerous to aquatic life, highly toxic to bees

Decrease 4E
Warnings: Toxic to aquatic organisms such as stone flies, water fleas and shrimps, can affect population diversity

Altosid Pro-G

Aquabac 200 G / CG granules

Top of the descent

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

What is in Cayman’s mosquito sprays?

Permethrin – insecticide in drugs used to treat scabies and lice.
Chlorpyrifos – pesticide attacks the nervous system of pests and insects. Classified as moderately dangerous to humans by the World Health Organization.
Pyrethrins – insecticide targets the insect nervous system. This class of organic compounds is biodegradable and its toxicity to humans is considered to be low.
Malathion – insecticide approved for treating head lice. Is considered to be of low toxicity to humans.
Methoprene hormone does not kill insects, but rather inhibits their life cycle and prevents maturity and reproduction.
Spinosad – insecticide used to treat fleas and head lice.
Deltamethrin – compound of a group of pesticides that are highly toxic to aquatic life. While it is generally considered safe for humans, it is neurotoxic and should be avoided.
Bacillus thuringiensis, subspecies israelensis – bacteria for the biological control of mosquito larvae.
Temephos – larvicide used to treat insect infested waters such as mosquitoes.
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 side effects such as hair loss and death in cats.
n-Octyl Bicycloheptene Dicarboximide – The ingredient has no inherent pesticidal properties, instead it helps increase the effectiveness of pyrethroid ingredients.
Piperonyl butoxide ingredient has no pesticidal properties, but rather helps to improve the effectiveness of certain ingredients.

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