Floodwater mosquitoes (Aedes vexans) numbers continue to drop according to our trap counts though they remain troublesome in some forested areas. Raines in excess of 2.5” around the 4^th of July weekend is likely to produce one or more floodwater mosquito broods around the 3^rd-4^th week of July if present temperatures remain warm. The severity of floodwater mosquitoes will depend on warm temperatures and any additional rains during our water treatment control efforts over the next 2 weeks. Crews are presently treating standing water areas with Bti and oil solutions.

Culex mosquitoes have been increasing in numbers typical this time of the season. Because gravid trap Culex numbers were at 2002 levels we began our adulticiding (spraying at night) program on June 30^th & July 1. Spraying began in the Townships of Northfield, Wheeling, Maine, Barrington and Hanover. Areas sprayed included residential areas along the Des Plaines River on the East portion of the District with high floodwater mosquito populations and high Culex gravid trap numbers. Other areas included forested areas with high nuisance mosquito problems. Following adulticiding both our gravid trap numbers and New Jersey light traps counts did not indicate further need of adulticiding. Nuisance mosquitoes have been decreasing consistently.

AFTER THE RAINS…:

It is extremely important that villages encourage residents to continually inspect their properties for standing water on at least a weekly basis. Typically after heavy rains, more ground level water sites become available for Culex egg laying as opposed to the subterranean production areas like catch basins during drought periods. NWMAD crews typically focus most of their Culex eradication efforts inspecting/treating ditches & culverts, detention/retention ponds, building foundations and heavily vegetative or organically polluted wetlands. Nuisance floodwater mosquitoes may be produced from almost any flooded, vegetative low area, river overflow areas, and even turf grass areas prone to flooding. The limiting factor in mosquito production from ground level sources is the amount of treatments we can perform before the mosquito completes its aquatic life cycle and the length of time water remains in such areas before evaporating or soaking into the ground.

DIRECTOR’S NOTE: The heavy rains we are experiencing now are a departure from weather conditions that happened during the 2002 WNV epidemic year in Northern Illinois. In 2002 at this same time we were in drought conditions and nuisance floodwater mosquitoes were at extremely low levels. The lack of nuisance mosquito biting last year may have contributed to the public’s misperception that there are no mosquitoes and WNV was less of a risk. It’s possible that if the public perceived less risk they may not have practiced appropriate mosquito avoidance methods. If weather conditions continue in 2003 we may likely have above average nuisance mosquitoes during the end of July and into August when WNV human cases would be expected.

CATCH BASIN TREATMENTS:

Catch basin treatment has been completed in the District. All known street and backyard catch basins have been treated throughout the District. Treatments were performed with 150-Day Altosid Ingots (methoprene). Door-hanger notifications were left at residences that we treated basins. Some of the difficulties we have encountered working with the village supplied maps were basins improperly positioned on maps and basins reported by residents (which we treated) that were not indicated on maps.

Villages are advised that if they didn’t supply catch basin clean-out schedules to NWMAD then it is possible that any basin maintenance procedures may remove our treatments and result in Culex mosquito producing basins!

MOSQUITO VIRUS SURVEILLANCE IN ILLINOIS

WNV positive mosquitoes have been reported in Lake and DuPage counties.

NWMAD has tested 460 Culex mosquito batches to date for West Nile Virus, St. Louis and now Eastern Equine encephalitis. No mosquito batches have been confirmed with West Nile Virus or St. Louis encephalitis. Mosquitoes testing positive in the District will be posted in this Newsletter as well as the NWMAD website www.nwmadil.com.

Seven U.S. states have reported WNV positive mosquitoes so far.

DEAD BIRD SURVIELLANCE INFORMATION:

As of this writing 395 dead birds have been reported to the NWMAD dead bird website. (http://www.nwmadil.com/Dead Birds.html). Currently four birds have tested positive for WNV from Cook (Oak Park), Henderson, Kankakee and St. Clair counties. Twenty-four U.S. states have reported WNV positive birds so far in 2003. Current information about WNV can be found on the state’s website www.idph.state.il.us/envhealth/wnv.htm or by calling 217-782-5830.

Cook County is testing crows and blue jays for WNV. Residents and Health Departments that have newly deceased crows or blue jays may call the County at (708) 492-2035 to inquire about testing procedures. Please be aware that limits have been placed on the number of birds to be tested for WNV from Cook County.

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, loose fitting, 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 unnecessary 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 for 5 days or longer like: tire casings, bird baths, flower pots and barrels that may produce mosquitoes. Neglected swimming pools may produce thousands of mosquitoes. Call the District to report large stagnant water areas that remain wet for more than 7 days.

Mike Szyska

Director