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| Mosquito Trapping |
| In order to more accurately monitor the mosquito population, Hillsborough
County Mosquito and Aquatic Weed Control maintains 75 different mosquito
traps strategically placed throughout the county. These traps are of varying
designs, designed to trap different types of mosquitoes from a variety of
habitats.
Our most common trap is designed by the Centers for Disease Control,
and is known as a “CDC Light Trap.” At the top of the trap,
a small cooler (purple) is filled with dry ice, which slowly evaporates
through a small hole drilled in the bottom of it. Mosquitoes home in on
this carbon dioxide trail, thinking it is the breath of an animal and
hoping for a blood meal. Just below it, underneath the disc-shaped protective
cover, a small light functions to attract the mosquitoes once they are
closer. As they approach the light, a tiny but powerful fan sucks them
into the net basket below, where they remain until our inspectors pick
up the collection the next day.
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Back at the laboratory, our inspectors empty the
trap collections, and observe the various specimens underneath a
microscope or magnifying lens in order to identify their species.
Using a standardized method of dividing and counting, they estimate
the overall numbers of mosquitoes of each species per trap. This
is very tedious work, but the information is used for a number of
important purposes, not the least of which is to determine the need
for treatment. Many of these trap sites have been maintained for
decades, and this historical information is critically important
in determining trends statewide. |
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Other Traps
Additionally, similar traps have been placed high in tree canopies, and
are designated as “Canopy Traps” for the purpose of trapping
the Culiseta Melanura mosquito. This species of mosquito is the primary
culprit in the transmission of Eastern Equine Encephalitis (EEE). While
this mosquito does not feed on humans, it transmits the virus from bird
to bird, spreading it throughout the wild bird population. Other species
of mosquitoes which feed on both birds and humans are then capable of
precipitating a major outbreak of the disease in the human and horse population.
Since this mosquito feeds on birds, the traps are placed high in the tree
canopy. We do not generally find the Culiseta Melanura mosquito in great
numbers here in Hillsborough County. Should their numbers begin to increase,
our canopy traps will alert us to the possibility of a disease outbreak
and we will take immediate steps to decrease the risk.
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Other uses for mosquito traps involve testing
mosquitoes which have recently ingested a blood meal. For this
we combine traps with sentinel chicken cages, as in the photo
of the trap shown below. The hungry mosquitoes enter the cage
from below, and once they have gorged themselves on blood, their
natural instinct is to fly upwards. By covering the cage with
screen and placing a bottle trap above the cage, we ensure that
the mosquito has nowhere to go but into the trap. These engorged
mosquitoes can then be crushed in the laboratory to obtain a blood
pool, which is analyzed for presence of virus. Additionally, should
one or more of the chickens test positive for Encephalitis virus,
records of the mosquito species found in the bottle trap at that
time will give us important information for research into which
species of mosquitoes are capable of transmitting which viruses.
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Similarly, the hanging chicken bottle trap, our latest innovation,
not only tells us if there are Culiseta Melanura mosquitoes in the
area, but the ones that have fed on the chicken in the blue barrel
can then be tested for the presence of Eastern Equine Encephalitis,
giving us results much more quickly than standard laboratory testing
of chicken blood. Remember, once the chicken has been bitten by
an infected mosquito, it must go through a four to fifteen day incubation
period before the antibodies will show up in the bloodstream. By
testing the mosquitoes as well as the chickens, we can get an “early
warning” and respond appropriately.
These are just a few of our research activities being conducted
by our “Special Projects” crew, whose charge it is to
find new and innovative ways to accomplish our mission.
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Back to Main Surveillance Page |
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