E AST O REGONIAN
WEEKEND, JULY 27, 2019
MOSQUITO
PATROL
A fog truck sprays a residen-
tial street in McNary. The driv-
er constantly monitors side-
walks and houses for open
windows and people outside
so that they are not sprayed.
West Umatilla Mosquito Control District began operations in 1972 and
covers a 515-square-mile area on the western edge of Umatilla County
STORY AND PHOTOS
by BEN LONERGAN
East Oregonian
HERMISTON — When Randy
Gerard started working as a sea-
sonal intern at the West Umatilla
Mosquito Control District more
than two decades ago, he couldn’t
walk through parts of the district
without getting swarmed by mos-
quitoes. Now Gerard is the man-
ager of the district and mosquito
populations are down to 20 to 25%
of where they were in the 1990s.
“In the 1990s it was not uncom-
mon to have to treat some of these
areas four to fi ve times per week;
now we can do them once or twice
a season and have a better result,”
Gerard said. “I believe the decline
in mosquito population is linked
directly with improvements to
technology and funding.”
The West Umatilla Mosquito
Control District began operations
in 1972 and covers a 515-square-
mile area on the western edge of
Umatilla County. The program
operates on an approximately
$800,000 annual budget funded
through a special property tax
district.
Within the district, mosquito
control can be broken down into
four main categories: the mos-
quito surveillance program, which
catches and monitors sources and
population spikes; the larvicide pro-
gram, which aims to kill mosquito
larvae before they become an issue;
the lab testing aspect, where dis-
ease testing occurs; and the adulti-
cide program, which utilizes chem-
icals to kill off adult mosquitoes.
“People are often most famil-
iar with the adulticide program,
the trucks driving around city
streets and your property at night,”
Gerard said.” However, it is really
our last resort; our goal is to use
other programs to eliminate mos-
quitoes before it gets to that point.”
The West Umatilla Mosquito
Control District monitors approx-
imately 980 documented larval
habitat sites and more than 1,200
catch basins and storm drains on a
weekly basis to help catch and kill
mosquito larvae.
Rylie Smith has been working
for the district for seven years in
both the larvicide and adulticide
programs. During peak mosquito
season Smith begins work at about
5 a.m. to maintain existing mos-
quito sources and search out new
sources. Each day he checks up
on reported outbreaks and treats
infested areas with a variety of
chemicals.
“When I arrive for the day, I try
to fi nd a place where I can access
as many sites as possible. I’ll check
to see when I last sprayed and
check dip cups for larvae,” Smith
said. “Everyone is pretty accepting
of us coming out to work; the only
real issues come up when property
changes hands.”
One of the leading sources of
CLOCKWISE, FROM TOP LEFT: Randy Gerard monitors wind speed prior to beginning his spray route. Factors, such as temperature and windspeed,
play heavily in when and where fogging trucks can spray. A mosquito trap hangs from a tree near Hermiston. The traps use sublimating dry ice to
create CO2, which attracts mosquitoes. Mosquitoes are then sucked in by a fan and captured in a vessel for testing. Andrew Ross (left) and Rylie
Smith use dip cups to check a small body of water for mosquito larvae. A dip cup holds mosquito larvae found on a farm property just outside of
Hermiston. The newly discovered body of water is added to mapping software so that it can be monitored and treated more regularly.
mosquito habitat in the district is
fl ood irrigation. When landowners
fl ood fi elds it often leaves behind
standing water that can provide a
perfect habitat for mosquito lar-
vae. While the district makes some
effort to educate people about pres-
surized irrigation systems, they
lack the funding to help secure or
subsidize grants to make improve-
ments more affordable.
“Being in the desert as we are,
the primary sources of water are
artifi cial sources, fl ood irriga-
tion, ponds, and poorly maintained
swimming pools,” said Gerard.
“We use the results of our sur-
veillance program to help fi nd and
treat outbreaks before the mosqui-
toes become adults.”
The district utilizes a network
of about 100 mosquito traps, 28 of
which are set at the same locations
while the other 72 rotate through
the coverage area on a weekly
basis. The traps consist of blocks
of dry ice in an insulated container
that vents CO2 to attract mosqui-
toes. Mosquitoes are then swept up
by a small fan into a collection con-
tainer to be tested. Traps are typi-
cally set and collected two times
per week in an effort to monitor
populations of Culex mosquitoes.
Culex is a specifi c genus of
mosquito that, while not usually
the ones seen swarming outside,
are the primary disease-carrying
mosquitoes. By catching Culex
mosquitoes the district can test
them for West Nile virus, St. Louis
encephalitis and Western Equine
encephalitis, as well as monitor
their prevalence in a given area.
While the testing can be done
in house by the district, or through
Oregon State University, positive
results must be sent to OSU to be
retested before a case can be con-
fi rmed. The district prefers to test
in-house so that results can be
acted on more quickly, with a 3-
to 5-day turnaround to send to the
lab. With this lead time, the dis-
trict can get a jump on fogging or
aerial spraying to attempt to kill
off Culex mosquito populations in
areas where a positive result has
surfaced for one of the diseases.
Although the district was
founded to deal with Western
Equine encephalitis, they shifted
their focus primarily to the mon-
itoring and treatment of West Nile
virus in 2005. According to Ore-
gon Health Authority, roughly one
in fi ve people infected with West
Nile virus may show signs of the
disease, with the most severe risk
posed to individuals over the age of
50 and people with immune-com-
promising conditions.
Once an outbreak of adult mos-
quitoes has been established, fog-
ger trucks equipped with spe-
cialized spraying technology are
driven through affected areas to
spread a mosquito control chem-
ical called Sumithrin. Sumithrin,
paired with the spray technol-
ogy run by the district, is specif-
ically targeted for mosquitoes,
however, precautions are taken
to avoid exposure for other ani-
mals, according to fi eld supervisor
Andrew Ross.
“We do our best to track down
organic farming operations and
work with them to establish man-
agement plans,” said Ross. ”Addi-
tionally we do everything we can
do to avoid bees and bee boxes by
not spraying near them and spray-
ing when bees are not active.”
Spraying typically starts at sun-
set and takes into account wind
speed and temperature to decide
both when and where trucks can
spray. The district has a fl eet of
four trucks equipped with the
spray technology that roam city
streets, country roads and farm
property at dusk.
Recently, the district has pur-
chased and begun exploring the
use of unmanned aerial vehicles
(UAVs) to add to their adulticide
fl eet. While the district is still
working on the permitting and
training to put drones into circu-
lation, they see promise in the use
of the technology to reach diffi cult
locations.
“Parts of our coverage area are
densely covered and we are unable
to get trucks in, and we are forced
to use planes to spray adulticides,”
Gerard said. “UAVs offer the abil-
ity for us to access these areas in a
cheaper and more targeted manner.”