In NEON tick drags 2014–2024, blacklegged nymph counts were lower and lone star adult counts higher on dry sampling days, and a dry summer did not lower next-year counts

Question: do NEON tick drag counts follow air dryness (vapour pressure deficit, VPD), and does a dry summer lower the next year's ticks? Data: the public NEON tick Darwin Core Archive (13,773 plot visits at 46 US sites, 2014-2024, including zero catches) and NASA POWER daily weather at each site. Methods: we made season-, plot- and effort-standardized annual density indices per site and species-stage. A pre-specified panel test related the indices to within-site anomalies of previous-summer (Jul-Sep, t-1) and current-season (Apr-Jul) VPD and winter temperature, with site effects, site trends, permutation tests and Holm correction. A post hoc test compared plot visits within the same site-year with the sampling-day VPD anomaly. Results: a dry previous summer did not lower counts (lone star nymphs -1% per SD, p_perm = 0.89; blacklegged nymphs +19%, opposite sign). Drier current seasons had lower nymph indices (lone star -13% per SD, p_perm = 0.08; blacklegged -14%, 0.11; all ticks -9%, 0.09), stronger with year effects for lone star nymphs and all ticks, but no test passed Holm correction. On drier sampling days, blacklegged nymph counts were lower (-15% per 0.36 kPa, 95% CI -23 to -6, p_perm = 0.002) and lone star adult counts higher (+14%, +4 to +25, p_perm = 0.018); lone star nymphs, dog tick adults and all ticks had no clear relation. Thus drag counts contain a species- and stage-specific questing response to weather, not only population change. Our independent trend method reproduced the site trends of SCI 0c852071 (r = 0.997, 41 pairs) and recovered injected declines without bias. Network trends were near zero (lone star nymphs -2.4%/yr, 95% CI -13 to +10). Species appeared at sites after 3 or more empty years more often than they were lost (11 vs 3-4; p = 0.06-0.12). Within plots, native ticks did not decrease where Asian longhorned ticks increased (rate ratio 1.03, 0.89-1.19). Limitations: the sampling-day test is post hoc; weather is about 50 km reanalysis, not plot microclimate; 7-20 sites and 10-11 years per response.

ticks · NEON · Ixodes scapularis · Amblyomma americanum · vapour pressure deficit · questing behaviour · drag sampling · population trends · weather · range expansion · Haemaphysalis longicornis · replication · vector surveillance