NUISANCE MOSQUITO CONTROL

Previous periodic rainfalls and the 3” rainfall that fell on August 6-9 throughout Northern Cook County will result in a sizable, biting, floodwater mosquito (Aedes vexans) population near the weekend of the 18^thdepending on temperatures. Floodwater mosquitoes are more aggressive day & night biters that will be more noticeable to the residents of the District than the timid, nocturnal Culex mosquitoes over the past 6 West Nile virus years. Aedes vexans has not been implicated as a very competent WNV mosquito vector to humans. Indeed, during the 2002 WNV Chicago land epidemic, a similar floodwater mosquito situation occurred at the end of August in Northern Cook County resulting in a sizable, biting, Aedes vexans population at the beginning of September. During that period of time, however, human WNV infections were decreasing in our District instead of increasing as you would have expected if this nuisance floodwater mosquito actually was a significant contributor to human infections.

NWMAD crews are actively treating all types of mosquito larvae infested floodwater areas with methoprene pellets. This will be an ongoing process given all the floodwater sites after this major rainfall event. Floodwater mosquito numbers will be significantly reduced by control efforts but untreated floodwater areas outside NWMAD territory will also contribute to the problem since this species can fly considerable distances in a single night!

DIRECTOR’S NOTE: Biting floodwater mosquitoes that that are very annoying will likely alarm the public as human WNV infections are also concurrently reported by health officials. Since it is unlikely that the residents of the District will be able to identify what mosquito species is actually biting them it would still be most prudent to encourage mosquito avoidance, control and self-protection to reduce the risk of infections. Please see NWMAD mosquito protection advice at: http://www.nwmadil.com/protecting yourself.htm. In 2002 it was interesting to note that the significant annoyance of biting floodwater mosquitoes may have actually helped reduce human WNV infections since people where then more apt to practice mosquito protection, control and avoidance more so than if less noticeable Culex mosquitoes were biting them!

CULEX MOSQUITOES

Culex mosquito numbers collected from gravid traps have been relatively stable at below average numbers than normally expected at this time of the season. It is still likely that their numbers will increase if the warmer temperatures continue to prevail. Elevated temperatures accelerate Culex development in stagnant water areas as well as the risk for WNV transmission. Control efforts and periodic rainfall wash-out events have helped stabilize numbers of these mosquitoes. Residents are strongly advised to inspect & eliminate all stagnant water areas from their properties that may produce these mosquitoes every week through the months of July-September. Any container that holds water and organic debris for greater than 7 days can produce many of these mosquitoes.

Stagnant water mosquito producing sites (detention/retention ponds, ditches, building foundations & container sources) will be treated with the insect growth regulator methoprene (Altosid).

Two thirds of the second treatment round of street catch basins in the NWMAD has been completed to date. Catch basins are treated with a 150-Day methoprene formulation.

MOSQUITO VIRUS SURVEILLANCE IN ILLINOIS

The Illinois Department of Public Health (IDPH) reports: 10 counties with mosquitoes or birds testing positive for WNV. There are 7 human cases (1-Cook County (Evanston), 1 Suburban Cook County) of WNV and 274 WNV positive mosquito samples reported from Illinois. Thus far IDPH has only reported 2 birds infected with WNV.

NWMAD has tested (VecTest/PCR) 567 batches of mosquitoes for West Nile Virus, St. Louis and Western Equine encephalitis. Fifty seven WNV infected batches of mosquitoes have been collected in NWMAD gravid traps to date. Mosquito batches testing positive in the District are posted at the NWMAD website http://www.nwmadil.com/VECTEST1.htm.

DIRECTOR’S NOTE: WNV infected mosquito distribution in Illinois is less extensive in 2007, thus far, compared to previous WNV years! The exact reason for this is not certain but could be due to a number of contributing possibilities including: poor 2006 overwintering survivorship of Culex mosquitoes, some below normal temperatures in the spring, or periodic rainfall events washing out typical stagnant water Culex habitats. The latter possibility is most consistent with previous WNV years and increased virus activity following warm, dry periods during the months of July-September and this has not been observed in 2007 to date. The delayed start of WNV activity in Illinois is a very good thing! Anything postponing/interrupting amplification of the virus in the mosquito and bird populations has the potential to reduce human infection rates. However, the summer mosquito season has not ended, and predicted warm temperatures in August-October, has in some years resulted in extended WNV activity.

ADULTICIDING (Night Spraying Operation):

Targeted, focal adulticiding has been performed (Aug. 1-2) in the Townships of Wheeling, Northfield (western third), Maine and Elk Grove in areas where WNV activity was repeatedly detected via mosquito virus surveillance. Continuation of adulticiding is likely if virus activity continues to be demonstrated in the mosquito population or nuisance mosquitoes become excessive and weather conditions are favorable.

Nightly spraying schedules can be viewed at the following website: http://www.nwmadil.com/nitespry_map.html. Alternately, a recorded phone message describing our scheduled nighttime spray program can be reached at (847) 537-2306 and pressing “5” on your telephone keypad. More information regarding our Adulticiding program may be viewed at: http://www.nwmadil.com/Night Spray info1.html

REDUCING THE RISK OF MOSQUITO BITES:

Avoid outdoor activity if possible from dusk to dawn when the mosquitoes bite the most. If you do go out wear light colored protective clothing and insect repellent (always read label warnings and directions). Make sure mosquitoes do not enter homes through unscreened or broken doors or windows. Residents are encouraged not to create mosquito harborage areas. Make sure tall grassy areas are trimmed and other vegetation is cut back. If plants must be watered do so in the morning so the vegetation and soil has a chance to dry making it less attractive to mosquitoes. Empty any containers holding stagnating water like tire casings, tarp covers, birdbaths, flower pots and barrels that may produce mosquitoes. Un-maintained swimming pools may produce thousands of mosquitoes. Call the District to report stagnant water areas that remain wet for more than 7 days. Additional mosquito avoidance/control practices may be found at the District’s website: www.nwmadil.com.

Mike Szyska

Director

PLEASE FORWARD THIS INFORMATION TO APPROPRIATE DEPARTMENTS AND AGENCIES.