There’s an old joke that mosquitoes are like family: They are annoying, but they carry your blood.
Mosquito season is starting to rev up across much of the
United States. And that means bug bites.
When a mosquito bites you, it pierces the skin using a
mouthpart called a proboscis to suck up blood. As it feeds, it injects saliva
into your skin that can cause a reaction — a bump and itching. But the pests
can also spread parasites like malaria and viruses like dengue, West Nile and
Zika.
So you might want to pause summer vacation planning and
consider what to look for in repellents, which keep bugs away from you, and
insecticides, which kill them.
WHAT MOSQUITO REPELLENTS WORK BEST?
The Centers for Disease Control and Prevention says that for
protection that lasts hours, people should look for ones with these active
ingredients: DEET, IR3535, picaridin, or oil of lemon eucalyptus. Those
ingredients are registered with the Environmental Protection Agency.
A note about oil of lemon eucalyptus: Lemon eucalyptus
essential oil has a similar name, but the agency does not recommend it because
it hasn’t been tested for safety and is not registered with EPA as an insect
repellent.
Likewise, the CDC doesn’t endorse other “natural” products
that haven’t been evaluated.
WHAT OTHER STEPS CAN YOU TAKE TO AVOID MOSQUITO BITES?
Repellents are one line of defense against bugs, but there
are others: Wear long sleeves and long pants. Avoid going out at dusk and dawn,
when some types of mosquito tend to be most active.
Silvie Huijben, an evolutionary biologist at Arizona State
University, helped develop an online game to help children understand how to
protect against mosquitoes, which emphasizes another prevention strategy:
“Mosquitoes need water to breed in,” so it’s important to
make sure to get rid of standing water — including buckets of water or kiddie
pools left undisturbed in the yard for a week or more, she said. “Make sure
you’re not the one contributing the local mosquito problem, that you’re not
breeding mosquitoes on your property.”
You can also treat clothes and outdoor gear with a pesticide
called permethrin to ward off mosquitoes and other unwelcome pests.
HOW INSECTICIDES ARE TESTED
The Centers for Disease Control and Prevention operates a
mosquito lab in Fort Collins, Colorado, where it evaluates insecticides, but
not repellents.
To test these kinds of products, the researchers coat the
inside of a bottle with a given dose of an insecticide ingredient, then put
mosquitoes in the bottle — usually about 25. They see what percentage of the
bugs die within two hours and compare that with a nearby uncoated bottle
containing the same number of mosquitoes.
The test is widely used in the U.S. and also is increasingly
used around the world. It is considered simpler and less expensive than some
more complicated alternatives, including a test in which insecticide drops are
applied directly to mosquitoes.
Scientists typically repeat the experiments each season to
document changes in how the mosquitoes respond to insecticides, CDC officials
say.
Huijben said repeating the test is important because it has
limitations: Results can be thrown off by factors such as whether each bottle
was coated with exactly the same amount of chemical.
“I think we’re seeing a lot of noise in the data” which may
lead to false initial conclusions, said Huijben, who has compared resistance
testing approaches.
ARE MOSQUITOES BECOMING RESISTANT TO SOME CHEMICALS?
Just like bacteria can gradually develop the ability to
shrug off antibiotics, bugs can develop resistance to some of the chemicals
developed to kill and repel them.
Permethrin belongs to a class of insecticides called
pyrethroids, which have shown this kind of resistance.
Pyrethroids grew popular in the 1990s as replacements to
older pesticides and are commonly used to control adult bugs. Community
mosquito-control programs and farmers use the chemicals, but homeowners can
also find them on hardware store shelves.
In lab experiments, resistance varies by product and dose,
but in some tests ”none of them (mosquitoes) will die,” said Roxanne Connelly,
a CDC insect scientist.
CDC officials are working with state and local officials to
do more real-world field testing, including experiments in which mosquitoes
placed in cages outdoors are checked after an insecticide fogging truck passes
by.