Jeffrey Hahn, Asst. Extension Entomologist
A benefit of our cold, late spring has been that the primary biting mosquito in Minnesota, Aedes vexans, was delayed in its emergence until early June. However, they are out now and if you spend any time outside, they will find you sooner or later. Mosquitoes have been particularly abundant this year because of the frequent rainfalls we have received. As long as we received regular rain, we can expect to continue to battle mosquitoes. In addition to the annoyance of their bites, mosquitoes are capable of transmitting diseases to people, especially west Nile virus (there were 70 cases in 34 counties in Minnesota last year including one death) and Lacrosse encephalitis.
Photo 1: Mosquitoes are abundant when we have a lot of rain.
It is challenging to completely avoid mosquito bites but there are some steps you can take to minimize your exposure to them. It is important to remove or drain potential breeding sites for mosquitoes. Any kind of standing water, with a little bit of organic material, is a suitable place for mosquito larvae to live and develop. This can include, but not limited to, buckets, tires, cans, and children's' swimming pools. Even clogged gutters can be source for mosquitoes. The key is that the site contains shallow water and is left undisturbed. While this step helps to reduce mosquitoes that can be produced on your property, this does not impact mosquitoes that can fly into your yard from adjacent areas.
Try to avoid, when possible, being outside when mosquitoes are most common. Mosquitoes typically are most active and bite during the morning and evening, although they will take a blood meal from us anytime during the day if we are close enough to their resting sites around grassy and brushy areas, shrubs, and trees.
Also use personal protection to help prevent mosquitoes from biting you. Consider wearing protective clothes to cover bare skin including sleeves shirts, long pants, and socks and shoes. Ultimately, the best personal protection against mosquitoes is the application of repellents.
Photo 2: Using a repellent, like DEET, is the best defense against mosquitoes.
The most effective and long lasting repellent is DEET (N,N diethyl m toluamide). This product has an excellent track record of safety for the last six decades. It comes in different concentrations, ranging from 4% to 100%, offering protection from 90 minutes up to 10 hours. However, there appears to be a limit to how much protection increasing concentrations of DEET can provide. There is evidence that suggests that there may not be much difference between concentrations of 35% and 100%. Applications of no more than 30% DEET can be used on children and infants at least two years old.
There are several alternatives that are effective repellents. One is option is picaridin. Picaridin has long been used as a mosquito repellent in Europe and Australia. It sold in the U.S. as a 7% or 15% concentration (Cutter Advanced and Cutter Advanced Sport). It is comparable to lower concentrations of DEET in effectiveness. Picaridin is generally less irritating to skin and lacks a chemical odor and sticky feel. Do not treat children younger than two years old with this product.
There are a couple of botanically based repellents available. Oil of lemon eucalyptus (p-menthane 3,8-diol), Repel brand, is a plant-based repellent sold as a 40% concentration. It is comparable to products containing low concentrations of DEET. Bite Blocker containing 2% soybean oil is also option. Research has shown that this repellent can offer protect for about 90 minutes or about the same protection as a very low concentration (4.75%) of DEET.
Whatever repellent you choose to use, be sure to always follow all label directions so the product is used most effectively while minimizing potential hazard to safety.
People's frustration with mosquitoes often leads them to put their faith in a variety of dubious methods to combat these blood-sucking insects. However, people are typically disappointed in the results of these tactics. Caveat emptor (buyer beware) -- what sounds too good to be true usually is.
Insect electrocuters, also known as bug zappers, attract large numbers of insects. However, research has shown that mosquitoes makes up less than 5% of all the flying insects killed. The number of mosquito bites remained the same regardless of whether or not you used a bug zapper. Research has even showed that insect electrocuters do more harm by killing beneficial insects.
Mosquito traps use carbon dioxide to attract mosquitoes, but it is unlikely that they can remove enough mosquitos to reduce the incidence of mosquito bites in a given area. While they sometimes can trap an impressive number of mosquitoes, this is a percentage of the overall mosquito population around the traps. Under the right circumstances, these traps can actually draw more mosquitoes into a yard than what they actually collect. These devices are also usually expensive.
Photo 3: Beware of gimmicks that promise to get rid of your mosquitoes; they are unlikely to prevent mosquitoes from biting.
There are a variety of devices that use sound to repel mosquitoes. They may claim to imitate the sound of male mosquitoes or predators like bats or dragonflies, insects or animals that female mosquitoes are supposed to avoid. Unfortunately this doesn't repel them in practice. Research has tested many of these products; none reduce the number of mosquito bites. A female mosquitoes' urge to find a blood meal outweighs potential threats to them.
The Citrosa 'Mosquito Fighter' plant is genetically created by crossing an African geranium with the Grass of China (which contains some citronella, a mild repellent). These plants are pleasant smelling and will grow to a height of 12 feet if left unpruned. But despite their claims, research has demonstrated that these plants do not repel mosquitoes. Citronella candles can help to some degree but its effectiveness is limited to small, calm areas. Any wind will disperse the smoke, negating any effect the candles could have.
Purple martins and bats have been reputed to consume large numbers of mosquitoes. While there is generally nothing wrong with encouraging these animals, mosquitoes actually made up less than 3% of purple martins' diets and less than 1% of bats' diets. Larger-sized, flying insects, such as dragonflies, butterflies, crane flies, beetles, and moths are the most common meals for these animals. The presence of purple martins and bats does not diminish the number of mosquito bites.