ABUNDANCE OF WINTER TICKS (DERMACENTOR ALBIPICTUS) IN TWO REGENERATING FOREST HABITATS IN NEW HAMPSHIRE, USA

Abstract

Recent decline in New Hampshire’s moose (Alces alces) population is attributed to sustained parasitism by winter ticks (Dermacentor albipictus) causing high calf mortality and reduced productivity. Location of larval winter ticks that infest moose is dictated by where adult female ticks drop from moose in April when moose preferentially forage in early regenerating forest in the northeastern United States. The primary objectives of this study were to: 1) measure and compare larval abundance in 2 types of regenerating forest (clear-cuts and partial harvest cuts), 2) measure and compare larval abundance on 2 transect types (random and high-use) within clear-cuts and partial harvests, and 3) identify the date and environmental characteristics associated with termination of larval questing. Larvae were collected on 50.5% of 589 transects; 57.5% of transects in clear-cuts and 44.3% in partial cuts. The average abundance ranged from 0.11–0.36 ticks/m² with abundance highest (P < 0.05) in partial cuts and on high-use transects in both cut types over a 9-week period; abundance was ~2 × higher during the principal 6-week questing period prior to the first snowfall. Abundance (collection rate) was stable until the onset of < 0°C and initial snow cover (~15 cm) in late October, after which collection rose temporarily on high-use transects in partial harvests during a brief warm-up. The higher abundance of winter ticks on high-use transects indicates that random sampling underestimates tick abundance and relative risk of infestation of moose. Calculating an annual index of infestation of winter ticks on moose is theoretically possible by integrating 3 factors: the infestation of harvested moose in October, the length of the questing period, and assuming a stable collection rate during the questing period.