Insights on the phenology of the Asian longhorned tick (Haemaphysalis longicornis) using stored lipids.

Abstract

The seasonality of Haemaphysalis longicornis in the United States comprises overlapping life stages in the spring and summer. This is partially attributed to the ability of all stages to survive the winter. Physiological condition in ticks refers to nutritional reserve levels and is often used to characterize tick populations. To determine if lipids were suitable for estimating the physiological condition in H. longicornis, lipid content was measured in unfed laboratory-reared ticks for up to 480 d. The results showed that lipids decrease significantly over time in adults (36% at 183 d), nymphs (33% at 63 d) and larvae (28% at 102 d) and could be used to study the population structure of field-collected H. longicornis. Lipids extracted from field-collected ticks (March to October) were measured to determine if different groups or cohorts could be identified during the season. The spring nymph population included high- and low-lipid groups that partially overlapped in April and May. In larvae, the lipid content of ticks in the spring was significantly higher than in the fall, suggesting that active larvae in the early fall do not overwinter. The analysis of lipids in adults showed that high- and low-lipid adults were present throughout the season, suggesting a continuous influx of recently molted adults until the end of the adult season, where only low-lipid ticks are found. The analysis of physiological condition in the Asian longhorned tick demonstrated a complex univoltine structure with some overlap in adults from different years.