Temporal Detection Limits of Remnant Larval Bloodmeals in Nymphal Ixodes scapularis (Say, Ixodida: Ixodidae) Using Two Next-Generation Sequencing DNA Barcoding Assays

Abstract

Using next-generation sequencing DNA barcoding, we aimed to determine: 1) if the larval bloodmeal can be detected in Ixodes scapularis nymphs and 2) the post-moult temporal window for detection of the larval bloodmeal. Subsets of 30 nymphs fed on a domestic rabbit (Oryctolagus cuniculus Linnaeus, Lagomorphia: Leporidae) as larvae were reared and frozen at 11 time points post-moult, up to 150 d. Vertebrate DNA was amplified using novel universal (UP) and species-specific primers (SSP) and sequenced for comparison against cytochrome c oxidase subunit I barcodes to infer host identification. Detectable bloodmeals decreased as time since moult increased for both assays. For the SSP assay, detection of bloodmeals decreased from 96.7% (n = 29/30) in day 0 nymphs to 3.3% (n = 1/30) and 6.7% (n = 2/30) at 4- and 5-mo post-moult, respectively. A shorter temporal detection period was achieved with the UP assay, declining from 16.7% (n = 5/30) in day 0 nymphs to 0/30 in 3-d-old nymphs. Bloodmeal detection was nonexistent for the remaining cohorts, with the exception of 1/30 nymphs at 2-mo post-moult. Host detection was significantly more likely using the SSP assay compared to the UP assay in the first three time cohorts (day 0: χ 2 = 39.1, P < 0.005; day 2: χ 2 = 19.2, P < 0.005; day 3: χ 2 = 23.3, P < 0.005). Regardless of the primer set used, the next-generation sequencing DNA barcoding assay was able to detect host DNA from a larval bloodmeal in the nymphal life stage; however, a short window with a high proportion of detection post-moult was achieved.

Keywords: DNA barcoding; bloodmeal analysis; host identification; next-generation sequencing.