Evaluation of acaricide treatments to experimentally reduce winter tick load on moose

Abstract Quantifying the consequences of winter ticks ( Dermacentor albipictus ) on the body condition and life‐history traits of moose ( Alces alces ) is a challenge due to several confounding factors. We experimentally reduced tick load on moose calves by testing the effectiveness of 2 acaricide treatments: one using topical permethrin (5%) alone and the other a combination of a more concentrated topical permethrin (44%) and orally administered fluralaner (25 mg/kg). We evaluated changes in tick load, body mass, hematocrit, and hair loss severity and occurrence, from recaptured or resighted moose calves over winter in Québec and New Brunswick, Canada. Nearly all untreated moose (94%, n = 41) experienced hair loss compared to calves that received the combination of permethrin (44%) and fluralaner (41%, n = 37). Of treated moose that exhibited hair loss, only 22% had more than 5% damage and some already had hair loss at capture. Capturing moose later likely increased the probability of observing hair loss when resighting treated moose, although hair loss essentially remained lower for treated calves than for untreated calves. In untreated moose, tick load at capture tended to drive hair loss, but calendar date mostly drove hair loss severity, especially during April. There was no clear effect of topical permethrin (5%) on tick load, body mass, and hematocrit. Body condition simply decreased from January captures to spring recaptures, regardless of treatment. Our results suggested that combining permethrin (44%) and fluralaner effectively reduced tick load based on hair loss severity and occurrence. We cannot, however, disentangle the individual effects of permethrin (44%) and fluralaner. We discuss research implications and considerations of using such a treatment for reducing winter tick load.