Don’t let your guard down, says Marion Public Nurse Kathleen Downey, because mosquitos that carry the deadly Eastern Equine Encephalitis virus are still very much out there and populations aren’t likely to drop until our first hard frost.
The state initiated a third round of aerial spraying this week, which might lessen the presence of mosquitos to a degree; however, as Downey points out, “The threat doesn’t go to zero.” It’s that first hard frost – a minimum of 28 degrees for a minimum of three hours – when most mosquitos will disappear, but that could take until December, she said.
Still, according to entomologist Blake Dinius, there is no real “season” for mosquitos. Mild days in fall and winter can draw mosquitos out, he said. In fact, a 50-degree day well after the first frost can activate one human-biting mosquito, the northern house mosquito, known to carry West Nile Virus. Culex pipiens, Dinius said, “It’s one of the few mosquitos who overwinters as an adult.”
But even after that first frost, given the nature of EEE outbreaks, the entire region should expect an increased EEE threat next year as well, and quite possibly the year after that.
Is Aerial Spraying Effective?
With aerial spraying, the mosquitos must be flying when the fog is released from the air, and the insecticide cannot penetrate the tree canopy.
Dinius is an expert on mosquito- and tick-borne diseases. According to Dinius, the effectiveness of aerial spraying varies from very effective to somewhat effective to not effective at all. There are multiple reasons for this and a number of variables involved, including the weather, temperature, and the very nature of the insecticide.
Aerial spraying is used, for the most part, in order to reach areas inaccessible by truck for ground spraying. The pesticide that is used is called Anvil 10+10, a combination of the two ingredients Sumithrin and Piperonyl butoxid. The method of use, Dinius said, is called “ultra low volume”, or ULV, which atomizes the liquid into a fog that floats or drifts above the ground to reach mosquitos in flight. If the air is too cool, “it’s just going to drop out,” said Dinius.
The spray quickly breaks down an is essentially dissipated completely by lunchtime the following day. With ULV, Dinius explained, the amount of effective ingredient combined with water is extremely small – about a shot glass for every 8 acres. It’s a micro-dose, essentially.
“Nothing is going to be a hundred-percent effective,” said Dinius. Past sprayings have resulted in some significant reductions in the population of mosquito species that concern us most –like the cattail mosquito, the principal mosquito that passes EEE to humans and horses – but do not fully eradicate them.
“The effects (of aerial spraying) are sometimes zero,” said Dinius. “Sometimes it’s 44 percent effective,” he said, while another spraying might be 88 percent effective. “You end up with a mixed bag,” he said. “But because the threat is so grave… doing something about that to reduce the numbers, I think, is really, really important. Even if you had a 44 percent reduction, it’s better than nothing.
“The state really has to do something about it, and a 44 percent reduction in [mosquitos],” Dinius said, “you’ve got to take the chance because people’s lives are at stake.”
Is Aerial Spraying Safe?
The insecticide the state uses has been tested extensively and causes no health risks to humans and pets. The impacts on other species, Dinius said, is where studies are lacking.
“There’s not enough data collected on impact,” said Dinius. Most people immediately think about the impact on bees, which Dinius said is insignificant because bees are not active or flying at night and, once they become active again, the insecticide is mostly broken down. But the impact on other species is a concern to Dinius.
“In my personal opinion, it probably hits some really small moths,” said Dinius. “On micro-moths there is no assessment on those – they’re hard to find, hard to identify… How do you even determine if it had an impact on that?”
Obviously, the state must weigh the cost benefit analysis of spraying versus not spraying, despite the dubious effectiveness that may result.
What’s the Best Way to Repel Mosquitos?
At the individual level is where one can protect themselves the most from infected mosquitos.
Despite some people’s lingering concern with the safety of DEET, Dinius said there have been four deaths associated with DEET use over the past 60 years. None of those deaths were confirmed to have been caused by DEET exposure.
“That is squeaky clean safe in a world of – pretty much everything,” said Dinius. “It’s very, very safe.” For perspective, Dinius shared, 150 people around the world are killed every year by falling coconuts, while mosquito-borne diseases kill 1 million people. And DEET’s effectiveness cannot be overstated.
For a near 100-percent effectiveness, a mosquito spray only needs to contain 20 percent DEET as an active ingredient. Any more DEET than that does not increase its effectiveness in repelling mosquitos, Dinius said.
Other Effective Non-DEET Repellants:
Oil of lemon eucalyptus is effective at 30 percent as an active ingredient, but one must check the bottle of any type of mosquito repellant for evidence that it has been EPA registered and a number included as proof that the EPA has tested the product for safety and efficacy.
BioUD is another effective alternative to DEET, but a product must contain 7.75 percent to be considered effective.
How Do They Repel Mosquitos?
EPA-registered repellants, as Dinius put it, “They simply give these animals a stuffy nose.”
Mosquitos don’t use their vision beyond 10 meters, so they aren’t attracted to us because the see us; mosquitos sense us from the chemicals we emit – the carbon dioxide we exhale while breathing and talking, our sweat, body odors, and body heat. Which is why, Dinius said, it is true that a mosquito will be more attracted to a “burly grown man” than a child.
These smelly sprays we apply to ourselves don’t kill mosquitos, rather they interfere with the neurons and receptors located on the mosquitos’ antennae and on their mouthparts that detect the chemicals we emit. It confuses the mosquito. They have no idea what they are “smelling”.
What is Ineffective in Repelling Mosquitos?
Dinus said many of the products labeled “all natural” repellents are not tested for efficacy, so those products, he said, “You use them at your own risk.” If there is no indication that it’s been approved by the EPA then there is no guarantee that it is safe, let alone effective.
Citronella sprays and candles, those don’t work either, said Dimius, at least not to any acceptable level of repellency.
There are bracelets marketed as insect repellants, but the majority of those have undergone studies that prove they are effective zero percent of the time.
There was one bracelet, Dinius said, that sprays a chemical called metafluthrin, that worked “okay,” but the same cannot be said for those sonic emitters. Those do nothing to keep bugs away, he said.
“Natural” yard sprays are useless, Dinius said. And some other types of mosquito spray for yards provide minimal effectiveness.
“The sprays are very temporary,” said Dinius. “They last days to weeks. They’re not long-lasting like tick sprays.”
Save your money, said Dinius, and call the Plymouth County Mosquito Control Project instead. They might be hard to get a hold of sometimes, but they will come spray your yard up to eight times a year for free.
Did You Know…
Mosquitos are prehistoric and have been sucking for 200 million years. Mosquitos need nutrient-rich blood in order to produce eggs, but blood is not a food for mosquitos. Mosquitos eat leaf debris and plant nectar, and some species of mosquitos are actually pollinators. Only females bite in order to lay their eggs, which must be deposited in standing fresh water. Just the tiny bit of water in one soda bottle cap lying around your yard is enough water for a female to lay her eggs. If you have any of those flexible plastic gutter spouts in your yard, the standing water in one of those tiny ridges is also enough to host another generation of mosquitos. Mosquitos need water and are mostly aquatic creatures, spending three of their four life cycles in water. They don’t fly in temperatures below 60 degrees.
Blake Dinius is employed by Plymouth County as an entomologist educator. He gave an informational talk called “The Bugs That Bite You” on September 20 at the Marion Natural History Museum before a small audience. He can be reached by emailing bdinius@plymouthcountyma.gov, or by calling 774-773-3404.
By Jean Perry