(A) I. scapularis phenology in southern New England, Northeastern USA, based on Fish (1993) [66] (Westchester County, NY, USA) and Tsao unpublished data (New Haven County, CT, USA). (B) Seasonal timing of horizontal pathogen transmission from nymphs (cohort 1) to larvae (cohort 2) via a shared reservoir hosts. Also noted are the relevant parameters influencing spirochete transmission as modified from Randolph and Craine [219]; see text for explanation. (C) Non-systemic transmission may occur potentially when naïve larvae feed either simultaneously with or very soon after an infected nymph has fed; larvae must feed near the source feeding lesion. Shaded areas of the larval and nymphal host-seeking phenology curves in (A) indicate the period over which non-systematic transmission may occur.