Mosquitoes suck, so what to do about it
We in Saskatchewan are generally spared the most dramatic forms of suffering, mega disasters such as earthquakes and hurricanes; instead, we suffer continuous minor irritation from cold and wind and potholes and, when it finally warms up, mosquitoes.
Until recently, local mosquitoes were mainly irritants, but as the climate changes they are beginning to carry the dangerous illnesses common in warmer areas into the province, heightening interest in effective mosquito control measures.
One way to figure out how to limit mosquito bites is to figure out how mosquitoes find us. Scientists say mosquitoes use exhaled carbon dioxide to track us down. Extremely sensitive to minute changes in carbon dioxide concentrations, they can sense carbon dioxide in our breath from long distances. Upon encountering a carbon dioxide plume, the mosquitoes orient and fly upwind, arriving eventually near us.
A disruption of the carbon dioxide detection machinery of mosquitoes has therefore been a long sought after goal. According to an article in the University of California’s Science Today reported on the Environmental News Network, scientists there have identified three classes of volatile odour molecules that can severely impair, if not completely disrupt, the mosquitoes’ carbon dioxide detection machinery.
The odour molecules the researchers identified work by affecting the mosquitoes’ carbon dioxide receptors, which are located in tiny, antennae-like appendages called maxillary palps close to the mouths of the mosquitoes. The three classes of the odour molecules are:
- Inhibitor molecules that inhibit the carbon dioxide receptor in mosquitoes and flies.
- Imitators molecules that mimic carbon dioxide and could be used as lures for traps to attract mosquitoes away from humans.
- Blinder molecules that cause ultra-prolonged activation of the carbon dioxide sensing neurons, effectively “blinding” the mosquitoes and disabling their carbon dioxide detection machinery for several minutes.
The identification of economical odour molecules that can work even at low concentrations could be enormously effective in compromising the ability of mosquitoes to seek humans, thus helping control the spread of mosquito-borne diseases.
In the case of the “blinder” class of molecules, the researchers found that even a brief exposure to these odour molecules activated the carbon dioxide-sensitive neurons in mosquitoes for at least five and a half minutes, and evoked such a strong and prolonged response in the neurons that the mosquitoes’ responses to subsequent carbon dioxide stimuli were severely reduced for several minutes.
The research team released female mosquitoes in a large enclosed greenhouse that contained two hut-like structures with carbon dioxide-emitting traps placed in each of them. The researchers then included in one of the huts a source of the ultra-prolonged odour blend in the form of a small fan-driven odour dispenser. They found that only a few mosquitoes entered this hut and made it to the carbon dioxide trap.
While we await the commercial availability of such controls, there are many existing methods used to prevent the spread of disease, or to protect individuals in areas where disease is endemic due to mosquitoes. These include:
- Habitat change that removes stagnant water and other mosquito breeding areas. This has to be done on a community-scale to be really effective, but it also helps to remove breeding areas like puddles of shallow containers of water in your yard. Maintaining natural wetlands, which is considered an environmental best practice, can conflict with this control measure.
- Prevent mosquito bites with insecticides, nets and repellents. Unfortunately, pesticide and repellents (such as DEET) have either known negative human or environmental effects or may have such effects so their use can be more damaging than the bites. Safer forms of prevention can include simple things like wearing long pants or building a screened-in porch so you can enjoy sitting outdoors.
- Natural predators can also be effective. The dragonfly nymph eats mosquitoes at all stages of development and is quite effective in controlling populations. A number of fish eat mosquito larvae, including goldfish, catfish, and minnows, and it may be possible to add them to ponds and marshes. Birds like purple martins also eat mosquitoes. In general, the more we can do to improve biodiversity the better.
For further information see Science Today.
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