Wellington‑Dufferin‑Guelph starts larvicide program

Mosquito control is one of those public-health jobs most people never notice unless something goes wrong. The basic idea is simple — stop mosquitoes while they are still larvae, before they turn into the biting adults that can spread West Nile virus. That is what Wellington-Dufferin-Guelph Public Health has now kicked into gear for the 2026 season across Wellington County, Dufferin County, and the City of Guelph. The stakes are not dramatic day to day, but they are real: fewer breeding sites means lower odds of infected mosquitoes showing up later in the summer. ### What is the program actually doing? The health unit is treating standing-water sites where mosquito larvae develop and where draining the water is not practical. That includes municipally owned catch basins, stormwater retention ponds, roadside ditches, sewage lagoons, and other persistent pools of water around the region. The point is to hit mosquitoes at the earliest stage, when control is easier and more targeted. (wdgpublichealth.ca) ### Why target catch basins? Catch basins are a big deal because they sit in the public sewer system, often along curbs or in places where rainwater collects and lingers. Turns out that makes them reliable mosquito nurseries. WDG Public Health says they are a key focus because they can hold water for long periods and can support mosquito species associated with West Nile virus. ### What kind of larvicide is this? (wdgpublichealth.ca) This is not truck-mounted adult mosquito spraying. The products are larvicides meant to stop larvae from developing into adult mosquitoes. WDG lists Altosid Pellets, Altosid XR Briquets, and VectoLex WDP for catch basins, plus VectoBac 200G and VectoLex CG for other standing-water sites. The applications are done by hand by licensed applicators or trained technicians, which tells you this is a targeted ground program, not broad aerial treatment. ### Is the local risk high? Not really — but “low” does not mean zero. WDG says the risk of becoming seriously ill from mosquito-borne disease in the region is very low, and most West Nile infections do not cause symptoms. But in rare cases the virus can cause severe neurological illness, and adults over 50 face higher risk of serious disease. That is why public health treats this as prevention, not panic response. ### Why start now? Because mosquito control works best before the worst part of mosquito season arrives. (wdgpublichealth.ca) WDG’s surveillance and treatment program runs through the warmer months, when mosquito activity rises and West Nile risk is highest in summer and early fall. Basically, if you wait until people are already getting exposed, you are late. ### What happened locally last year? The backdrop is pretty calm, but not empty. (wdgpublichealth.ca) WDG’s local surveillance summary says 2024 had no mosquito pools testing positive for West Nile virus and no locally acquired human cases. But in July 2025, public reporting in Guelph noted a dead bird that tested positive for West Nile, which is a reminder that the virus does circulate in the broader environment even when human cases stay at zero. (wdgpublichealth.ca) ### Why is there a formal notice at all? Ontario treats this as a regulated public-health pesticide program. The province requires permits and public notification for larvicide programs aimed at West Nile prevention on public land under municipal or board-of-health authority. So the notice is not just courtesy — it is part of the compliance structure for running the program. ### Bottom line This is routine, but it is not trivial. Wellington-Dufferin-Guelph is trying to keep mosquito numbers down before summer peaks, using targeted larvicide in the places mosquitoes breed best. (wdgpublichealth.ca) If the program works the way it is supposed to, most people will barely notice it happened — and that is kind of the point. (wdgpublichealth.ca) (ontario.ca)