Reducing tick density along recreational trails in Ottawa, Canada: results from an ecotone modification study using deltamethrin-treated and untreated woodchips

Abstract

Expanding tick populations and increasing Lyme disease incidence in Ottawa, Ontario, highlight the need for effective strategies to reduce human exposure in recreational areas. Ixodes scapularis is the primary tick vector of Borrelia burgdorferi sensu stricto (s.s.), the causative agent of Lyme disease in this region. We conducted a two-year experimental field trial (2022–2023) in Ottawa's Greenbelt to evaluate whether modifying trailside ecotones with woodchip borders could reduce questing tick density. Twenty 50-m trail segments across two sites were randomly assigned to intervention groups: untreated woodchip borders, deltamethrin-treated woodchip borders, and ten assigned to untreated controls. Pre-treatment tick drags were conducted at the start of each study year, and environmental variables (canopy cover, canopy type, soil moisture, leaf litter depth) were recorded. Post-intervention sampling was performed weekly for six weeks during peak nymphal activity (June–July). The effects of deltamethrin-treated or untreated woodchip borders on tick density compared to controls were analyzed using mixed-effects negative binomial regression accounting for study design. A total of 440 ticks were collected, including 322 adult and nymphal I. scapularis. Of 293 ticks tested, 34.5 % were positive for B. burgdorferi. Treated woodchips reduced I. scapularis adult and nymph density by 99 % (incidence rate ratio (IRR) = 0.01, 95 % CI: 0.001–0.08) relative to controls, while untreated woodchips achieved a 48 % reduction (IRR = 0.52, 95 % CI: 0.34–0.78). This study demonstrates that modifying trailsides with woodchip borders, deltamethrin-treated or untreated, substantially reduces questing tick density, offering a tool for integrated tick management in recreational settings.