Control starts at home: Ways to combat mosquitoes this summer

June 24, 2015

Mosquito control
In order to maintain control of Portland's vector mosquito population, it is essential that homeowners maintain their personal environments.

Although summer didn’t officially begin until last weekend, summer-like temperatures of 80-degrees plus arrived weeks ago. The warmer, drier weather is driving a sharp increase in some mosquito species, Multnomah County’s Public Health ecologist said this week.

“We’re seeing it already this year,” says Bekah Sudia, who works to identify mosquitoes and the harmful human-prone viruses they carry. “With the earlier, warmer temperatures, we have more vectors.”

The metro region hosts two main mosquito species: floodwater — a nuisance species hatched mainly from the spring runoff — and vector, a disease-ridden species that can be harmful to humans.

The abnormally warm and dry winter lowered the spring runoff and decreased the population of the floodwater species. At the same time, high temperatures are driving a drastic increase in vector species. This is projected to only grow over the summer.

Because of the potential problems this poses to the Portland-metro area — including a possible resurgence of  West Nile Virus —  Vector Control workers like Sudia urge citizens to do their part.

“A lot of people tend to forget that it’s actually an issue,” says Sudia, stressing that the control of vector mosquitoes will only come if citizens take action towards individual homeowner prevention. “It really starts in your own backyard.”

Help eliminate breeding grounds

The most important step residents can take is to eliminate all traces of standing water from their surrounding property. Stagnant pools provide ideal breeding grounds for vector species to hatch and multiply, especially with this summer’s heat.

Quick actions such as surveying the backyard for leftover rain water or unchanged pools of water (i.e. dog bowls, birdbaths, empty tires, kiddy pools...etc) can help decrease species growth and limit the possibility of developing diseases, such as West Nile Virus.

The sample above, taken from one of Portland's neighborhood streams, contains juvenile mosquitoes in various stages of life. Encircled in red is a pupa (the final stage before adulthood) and shown inside the blue circles are larvae.

Another effective way of controlling the mosquito population is through widespread use of mosquitofish — a free service provided for the general public by the county. The fish are a small species that feed on mosquito larvae and can be placed in enclosed bodies of water to reduce the mosquito population in an immediate area, either in large quantities — such as in an enclosed pond — or in small barrels that contain excess water. To obtain specimens one has only to contact Vector Control 503-988- 3464.

Installing mechanical pond pumps is also an effective preventative measure, as mosquito eggs are unable to hatch in turbulent water. Though most wouldn’t think of it first hand, reporting dead birds to Vector Control for disposal (within 24 hours of death) can drastically decrease the transfer of diseases, as birds become reservoirs for vector development.

“If everyone did it, we’d see a drop,” says Sudia, acknowledging that while it may be unrealistic to expect every citizen in Multnomah County to abide by such principles, an increase in effort from the general public is what will make the difference this summer. “We really rely on people for that because...focusing on their own environment, their own where a lot of what we can’t control comes from.”

Team working nearly year-round to reduce larvae

Multnomah County’s Vector Control team works to monitor the ever-changing species and hatches. Jim Stafford, the lead Public Health vector specialist for the county, works on a small  team monitoring hotspots. He describes their jobs as “the pebble in the shoe;” one that goes virtually unnoticed by the general public until a problem arises that requires their immediate attention.

“We’re not out there visible with spray trucks, you know, driving down neighborhood streets like where I grew up,” says Stafford. “A lot of the work we do is behind the scenes.”

Mosquitofish are an invasive species that will, if released into an open body of water, outcompete the native inhabitants. When used for mosquito control, they must be contained in a closed basin or pond.

The team focuses on mosquito larvae, working to gain control of the population and identify the different species before they become a widespread issue. The work ranges from taking field samples of larval species or treating each of the 7,000 sedimentation manholes throughout the city to reduce population growth, to responding to any public complaints and making house visits. The five-member team covers the entire county.

“It’s a small profession...but we’re all pretty close,” says Stafford. He considers himself lucky to have a job that allows him to work outside and simultaneously help the people of Portland maintain an enjoyable quality of life. “You want to be able to enjoy the great weather we have here without being chased indoors by mosquitoes. We’re looking at all options of controlling the problem, then kind of resorting to chemicals as a last resort,” he says.


Early on a recent Monday, Jim Stafford steps off a crumbling creek bank into the plant-ridden water, decked in a white cloth one-piece suit and over-the-knee rubber muckers. He extends a long white rod into the water, dips the cupped-tip in and draws it back, examining the contents for mosquito larva. At least five wiggle around in the basin; a lot for late June.

Back in his work truck, Stafford voices his wish for increased city-wide awareness, acknowledging that this week (June 21-26th) has been dubbed “Mosquito Awareness Week” by the American Mosquito Control Association. “Eventually it’d be nice to have larger exposure,” he says, such as hosting a tire drive to cut down on the potential breeding sites. Just getting the word out, Stafford believes, is key.

Stafford and the county's four other vector health specialists are slowly chipping away at the 7,000 sedimentation manholes that they have to treat each summer. They use a chemical called Altosid that prevents the mosquito larvae from fully maturing.

Ultimately, the Vector Control’s message to the general public hasn’t changed this summer, the rise in temperature only makes it more imperative: Do what you can to help prevent the development of dangerous and pesky mosquito species; it’s going to take increased effort from the entire community, and Vector Control is here to offer any applicable services necessary.

“It’s constantly evolving and we have to be able to evolve with it,” reminds Sudia of the demands of the growing mosquito population. “We can’t just go ‘Same as last year.’ ‘Cause it’s not.”