Evaluating a novel core-and-perimeter delimiting trapping survey design for insects. I. Field experiment.

We propose a novel "core-and-perimeter" delimiting trapping design for invasive insects, improving upon the ubiquitous fully trapped square grids using regular spacing. The core-and-perimeter design has traps near the epicenter and in a perimeter set at a distance to result in zero captures, to directly set the population boundary. We compared the core-and-perimeter and fully trapped designs in a mark-release-recapture experiment with Ceratitis capitata (Weidemann) (Diptera: Tephritidae) in Hawaii in 2022. Each design had 4 repetitions with 4 separate releases of flies and 6 collection days from 1 to 14 d after release. The square fully trapped grid had 20 core area traps plus 79 other traps in 0.92 km2, plus 24 "sentinel" traps beyond. The circular core-and-perimeter grid had 20 core traps, and 108 traps in a 220 m-wide perimeter, set 500 m from the release point (smaller than the recommended radius). Slightly more flies on average were captured in the fully trapped treatment but proportional captures in common locations were similar. Flies were caught in the sentinel traps in every replicate of the fully trapped treatment. Four percent of captures occurred in the perimeter of the core-and-perimeter treatment on average. Trap usage rate for the fully trapped design was 67%, while for the core area of the core-and-perimeter design was nearly 94%. Overall mean daily dispersal distance was 96.3 m, and the regression-based 99th percentile of total distance was 700 m. Results supported the potential of the core-and-perimeter design and demonstrated 2 fully trapped design disadvantages-trap inefficiency and egress potential.