The year’s first mosquitoes have tested positive for West Nile Virus.

The North Shore Mosquito Abatement District (NSMAD) is gearing up to stop mosquitoes.

What does that mean?

With a budget of $1.5 million, NSMAD
is charged with reducing the risk of disease and annoyance from mosquitoes for 330,000 people in Evanston and 13 other North Shore communities.

NSMAD, funded by Cook County property taxes, monitors weather patterns and mosquito and tick populations, tests bugs for disease, provides community education and decides when to spray or take other action.

To kill adult mosquitoes during 2018, NSMAD sprayed 702 gallons of the pest-
icide Duet through a truck-mounted vaporizer. Over 22 nights, NSMAD covered 76,000 acres and more than 2,000 road miles.

Is that safe?

NSMAD Executive Director Mark Clifton points to federal approval of the active ingredients, particularly sumithrin, a pesticide known as a pyrethroid. “The United States Environmental Protection Agency is charged with studying the toxicity, persistence and environmental fate of mosquito adulticide products. According to the EPA, ‘When applied according to label directions, pyrethroids used in mosquito control programs do not pose unreasonable risks to wildlife or the environment.’”

For public events – twice in 2018 – NSMAD may also deposit a barrier of the pesticide Flit – the active ingredient of which is permethrin, a different pyrethroid – to reduce the mosquito population.

Beyond Pesticides, a nonprofit advocacy group, notes even though the Duet ingredient sumithrin is considered only slightly toxic, the overall components of Duet raise concerns as a likely carcinogen, neurotoxin, endocrine disruptor, contributor to kidney or liver damage and toxin for fish, bees and other wildlife; pretty much the same concerns for Flit.

Overall toxicity is a big question, according to a Beyond Pesticides March 2019 report. “The real threats of herbicides, fungicides, and insecticides are masked when EPA only tests active ingredients. … Based on EPA’s current policies, the agency does not require any testing on the health effects of pesticide products, as commonly applied, in the areas of chronic toxicity, carcinogenicity, mutagenicity, developmental and reproductive toxicity, or subchronic oral toxicity, inhalation toxicity, and neurotoxicity.”

Apart from human health issues, some might question why spray community-wide while insect populations, migratory birds and other wildlife are reported to be in steep and rapid decline.

The U.S. Fish and Wildlife Service has listed a once common local bee, the rusty patched bumble bee, as federally endangered. But the Illinois Department of  Natural Resources approved NSMAD’s spraying, saying it was unlikely to impact state-listed species, natural areas or the rusty-patch bee.

NSMAD’s Dr. Clifton says the mosquito spray – “about a shot-glass per acre” – will not hurt most other bugs: “The small amount of deposition on foliage does not affect non-target species, due to the extremely low volumes applied and the very short half-life of the material. Mosquitoes are small; therefore, the amount of material used is similarly very small. Within a few hours after treatment, most of the distributed material is degraded into non-toxic components.

“Treatments only occur at night, when mosquitoes are most active and most other insects are not active. Therefore dragonflies, moths and other insects are not likely to be impacted by adult control treatments.,” Dr. Clifton said.

Beyond Pesticides disagrees. “Because pyrethroids are toxic to all insects,” according to one of its pyrethroid factsheets, “both beneficial insects and pests are affected by pyrethroid applications. In some cases, predator insects may be susceptible to a lower dose than the pest, disrupting the predator-prey relationship.”

Regardless of when they are active, cocoons, caterpillars, moths and other creatures stay or live outdoors, where the insecticide is sprayed.

All night bugs are there somewhere.

Residents can opt out of spraying, in which case, the spray is turned off and on at their property line. This requires a doctor’s note. NSMAD will not consider liberalizing the opt-out procedures for people with
pollinator gardens or organic vegetables.

Dr. Clifton said a mosquito public health emergency occurs nearly every year, so there must be few exceptions.

Another debate is how long the insecticide persists in the environment, where it can continue to impact people or wildlife. While Dr. Clifton says most of the material is non-toxic within hours, Beyond Pesticides’ factsheet says sumithrin drops to one-half toxicity after one to two days in dry, sunny conditions, and may persist for weeks or months in dark, wet or still-air locations, like tunnels or silos.

Beyond Pesticides says, “Pesticide products containing pyrethroids are often described by pest-control operators and community mosquito-management bureaus as ‘safe as chrysanthemum flowers.’ While pyrethroids are a synthetic version of an extract from the chrysanthemum, they were chemically designed to be more toxic with longer breakdown times and are often formulated with synergists, increasing potency and compromising the human body’s ability to detoxify the pesticide.”  

Why the cost and effort to stop West Nile virus?

The Illinois Department of Public Health reports that in 2018, 176 people across Illinois were infected with West Nile, of whom 17 died.

NSMAD reports 16 Evanstonians were infected with West Nile virus during the last 10 years; no Evanston deaths are reported.

According to the U.S. Centers for Disease Control, eight of 10 people do not realize they have the virus, which causes flu-like symptoms, but one in 150 becomes seriously ill.

Not all mosquitoes carry West Nile Virus. Illinois has 76 species of mosquito, of which 20 are commonly found in this area. The Culex pipiens and Culex restuans are the primary vector (carrier) mosquito species here. The common floodwater, nuisance mosquitoes do not carry the virus.  

NSMAD acknowledges that killing adult mosquitoes is a last resort. “Adult mosquito control measures are the final intervention available when other control methods have failed to lower disease risk or reduce high nuisance mosquito populations,” says Dr. Clifton.

To manage mosquitoes at home, NSMAD encourages steps like dumping containers where water accumulates, using bug repellent and refreshing birdbaths weekly.

Ninety percent of NSMAD’s field program aims at killing mosquitoes in their larval stage with growth regulators, bacterial insecticides and surface oils. Mostly in the form of mosquito dunks and granular crumb, they are dropped in 43,000 catch basins (two to three times each) and 2,800 North Shore ponding sites.

This year, NSMAD has a truck-mounted turbine that can kill larvae wriggling in foliage. Dr. Clifton says the larvicide, based on naturally occurring bacteria, effectively targets mosquitoes.

Beyond Pesticides questions how these products, especially the growth regulator, affect frogs, bees and aquatic organisms, but agrees that larval controls are better
for humans and wildlife than adulticides.

“In most cases [Beyond Pesticides’] efforts are aimed not at eliminating all adulticide use, but raising the threshold at which it’s acceptable to spray in line with resident concerns and community values,” says Drew Toher, Beyond Pesticides’ Community Resource and Policy Director. “Our approach is that it’s only acceptable to spray when there is a sustained presence of a disease vector.”

Mr. Toher points to Washington, D.C., which has not sprayed in years, and Connecticut, which requires local municipalities to approve spraying unless a public health emergency has been declared.

Dr. Clifton says West Nile is more pervasive here: “Unfortunately the NSMAD reaches the conditions in Connecticut’s response level of four [public emergencies] by July in almost every single year.”

He notes in 2018, Connecticut (population 3.5 million) had 20 West Nile cases while Chicago (population 2.7 million) had more than 100.

Mr. Toher asks whether heavy investment in public education, combined with larvicides, reduces reliance on sprayed adulticide. It is up to the community to voice its preference, he says.

Anyone who would like to receive spray alerts, opt out with a doctor’s note, read about how to reduce mosquito breeding grounds at home or otherwise communicate with NSMAD may visit

Due to an editing error, as originally posted, the following paragraph from Beyond Pesticides’ factsheet was misattributed to NSMAD’s Dr. Clifton.