The Chester County Health Department (CCHD) operates a robust and proactive Mosquito-Borne Disease Program from April through October each year, focusing heavily on integrated pest management to suppress the threat of West Nile Virus (WNV). To assess risk and track virus prevalence, licensed environmental health specialists deploy between 32 and 40 specialized mosquito traps every week across various fixed and rotating sites determined by population density and past virus activity. The department relies on two distinct adult trapping technologies to capture different segments of the mosquito population. The first is the Gravid Trap, which features a modified toolbox containing a battery-powered fan positioned over a bin of foul-smelling, stagnant water; this setup mimics ideal breeding conditions to lure and capture female Culex mosquitoes—the primary vectors of WNV—after they have mated and are seeking a place to deposit their eggs. The second tool is the BG Sentinel or Host-Seeking Trap, a more conspicuous device resembling a mesh laundry hamper suspended near a blue beverage cooler filled with dry ice. As the dry ice sublimates into carbon dioxide ($CO_2$) gas and combines with an artificial human-scent lure, it replicates a living, breathing host, effectively tricking blood-seeking female mosquitoes into entering the trap net.
Beyond tracking flying adults, the CCHD aggressively targets mosquitoes in their aquatic stages through a field practice known as “dipping.” Using a simple measuring cup attached to a long, telescoping pole, technicians inspect standing and stagnant water in natural habitats like wetlands, ditches, and storm basins, as well as artificial breeding grounds such as abandoned swimming pools, discarded tires, and open buckets. All adult mosquito samples gathered from the field are given a preliminary count by CCHD staff before being shipped directly to the Pennsylvania Department of Environmental Protection (DEP) laboratory in Harrisburg for official identification and viral testing. Test results are returned within a week, giving the county precise data to share with local municipalities and dictate immediate, targeted intervention strategies.
When control measures become necessary, the CCHD prioritizes environmentally safe and localized methods to eliminate the pests without disrupting the broader ecosystem. Larval habitats are immediately treated using commercial-grade bacterial larvicides derived from natural soil bacteria, such as Bacillus thuringiensis israeliensis (Bti) and Lysinibacillus sphaericus (Ls), which eradicate mosquito larvae but remain entirely harmless to fish, amphibians, and other aquatic wildlife. For more sustained control, technicians may apply Insect Growth Regulators (IGRs) to disrupt the insect’s life cycle and prevent the pupae from successfully transitioning into flying adults. However, if testing indicates that WNV prevalence has reached a threshold that poses an immediate risk to public health, the department will pivot to adult mosquito control. These adulticide applications are executed exclusively by fully state-certified Public Pesticide Applicators using EPA-registered products, delivered either via highly localized backpack mist blowers for barrier treatments or through truck-mounted Ultra-low Volume (ULV) sprayers for broader community coverage. Ultimately, the CCHD emphasizes that public education and community cooperation are the most effective lines of defense, urging residents to routinely dump standing water on their properties to maintain “Bite Free Zones.” For specific questions, complaints, or to request product safety data sheets, local citizens can directly contact Environmental Health Supervisor Andy Heydt by calling 610-344-6243 or emailing aheydt@chesco.org.
