| Trends in Mosquito Populations
Early season mosquito populations had many people running for cover at dusk. Trap counts show
that the vast majority of these mosquitoes were likely Aedes vexans. These mosquitoes are noted
for biting aggressively shortly after sundown. In many areas, the public’s perception is
that mosquito populations have been decreasing. That is not necessarily true. Trap counts are
showing a drop in Aedes vexans, but the populations of Culex tarsalis have been increasing dramatically.
Culex tarsalis often bite throughout the evening hours and may be more of a “stealth”
bitter.
This presents the problem of the public not thinking of using personal insect repellents. Coupled
with this perception is the fact that a much higher number of mosquito pools (samples of 50 mosquitoes)
have been testing positive for West Nile Virus. Depending upon the temperatures as we near fall,
we could be seeing a high threat from West Nile Virus late into the season.
Managing Late Season Mosquitoes
When we hit mid-summer we often increase our use of adulticiding and reduce our efforts
in larval control. Since Culex tarsalis overwinter as adults, they may be breeding into the fall.
Well placed larvacides are still the most effective method of controlling mosquito numbers. In
areas where adulticiding alone is used, mosquito may drop substantially, but rebound in just a
few days. Public mosquito control programs that use larvacide in conjunction with adulticiding,
based on trap counts, frequently have much longer periods of control before the population start
to increase.
What do we mean by “well placed” larvicides, The typical site for larvicides has been
fairly permanent pond and pools of water that are open and visible. From larval survey work done
at SDSU, it appears as though Culex tarsalis may prefer temporary pools of water, especially if
there is vegetation such as grass partially covering the water. Large numbers of mosquito larvae
have been found in just a couple inches of water in the bottom of a ditch. Don’t overlook
low spots that may collect water for a couple of weeks. As well as the known areas in town, consider
checking areas a mile or two outside of town. The conditions favored by Culex tarsalis are often
more common in rural areas.
You can’t treat everything. Target your applications by dipping for larvae and only treating
areas where they are present. Continued larval treatments combined with adulticiding will greatly
assist in managing your mosquito populations into the fall.
Mosquito Trap Counts
Thanks to everyone who entered their trap count data into the Web-based mosquito populations graphing
program. If you would like to see how your counts compare to those in neighboring communities
to see if the trends you are seeing are showing up in other areas, please check: http://www.ces.sdstate.edu/mosqcount/
If you have mosquito counts and would be willing to enter them into the program. Please give
me a call or email me wilson.james@ces.sdstate.edu , and we will get you set up with access to
the program. The data entered over the season has helped us evaluate what is happening with the
mosquito populations across the state. If you have mosquito trap count data, please consider entering
it.
So far this season, there have been 256,000 total mosquitoes and 51,000 Culex tarsalis trapped
and entered into the program.
Quick Stops for Mosquito References
If you are looking for information on mosquito control don’t forget to go to:
http://sdces.sdstate.edu/westnile/ and click
on “Community control” in the upper right hand corner. You will find information that
we have gathered to assist you in your public mosquito control program.
Still trying to identify mosquitoes? Don’t forget an excellent mosquito identification key
located at :http://biomicro.sdstate.edu/Hildrethm/Mosquito/Index.html
It’s a Matter of Public Safety
Running a public mosquito control program can be difficult, but remember, with the threat
of West Nile Virus present in the state, the work you do is a very important public service. Keep
monitoring and treating mosquito adults and larvae into the Fall.
We can’t control every mosquito, so please remember to educate your public. The most important
prevention an individual can take against WNV is using personal insect repellent.
|
