In vitro assessment of entomopathogenic potential of Clonostachys rosea (Ascomycota: Hypocreales) against Ixodes scapularis (Acari: Ixodidae) and Dermacentor variabilis (Acari: Ixodidae) ticks

• Clonostachys rosea was isolated from field-collected Dermacentor variabilis ticks. • The fungus caused up to 70 % mortality in Ixodes scapularis and 30 % in D. variabilis . • Fungal infection led to impaired movement and cuticle damage in treated ticks. • Findings support C. rosea as a potential biocontrol agent for tick management. This study isolated and identified a Clonostachys rosea strain from field-collected tick samples in Nova Scotia, Canada, and investigated its entomopathogenic potential against Ixodes scapularis and Dermacentor variabilis . Ticks were collected from April to June 2023 through drag sampling and the fungus was isolated from dead or mycotic tick specimens. The isolate obtained from D. variabili s was subcultured from a single colony to obtain pure cultures. The fungus species was characterized through morphological and molecular analysis. The efficacy of C. rosea conidia was evaluated against lab-reared I. scapularis and D. variabilis unfed female adults using the adult immersion test. The C. rosea conidia (1 × 10 8 conidia/mL) caused approximately 70 % of mortality in I. scapularis and 30 % in D. variabilis female adults after 14 days post-infection. Conidia-exposed ticks showed physical damage, including claw and leg detachment, and loss of cuticle integrity. Our findings indicate that C. rosea is an entomopathogenic fungus that may be used for tick control. Because C. rosea naturally occurs in Nova Scotia, it is a promising candidate for biological control in regions with similar climate and environmental conditions, as well as a high prevalence of ticks and tick-borne diseases, such as the northeastern U.S. and Canada.