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

Authors: CATON, B - Animal And Plant Health Inspection Service (APHIS); FANG, H - North Carolina State University; HAIN, E - Animal And Plant Health Inspection Service (APHIS); KANDEL, NADYA - North Carolina State University; Nelson, Rosalie; PALLIPPARAMBIL, G - North Carolina State University; Manoukis, Nicholas

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2025
Publication Date: 6/14/2025
Citation: Caton, B.P., Fang, H., Hain, E., Kandel, N., Nelson, R.C., Pallipparambil, G.R., Manoukis, N. 2025. Evaluating a novel core-and-perimeter delimiting trapping survey design for insects. I. Field experiment. Journal of Economic Entomology. Article toaf095. https://doi.org/10.1093/jee/toaf095.
DOI: https://doi.org/10.1093/jee/toaf095

Interpretive Summary: "Delimitation" is often a key first step in the response to an invasive insect pest; it involves setting up traps to confirm the presence of the pest and to determine the potential extent of its spread. This study is the first in a two-part series that tests a novel approach to setting the trap positions for delimitation, which we term the "core-and-permieter" ("C&P") method. Under C&P traps are set up in an area around the first detection(s) and then a parimeter is set at a distance estimated to be larger than the spread of the population. In part 1 we describe results of "mark-release-recapture" experiments in Hawaii with Medfly to test the C&P approach in real life. We find that the method holds promise as compared to a "fully trapped" (FT) grid, which is a regular array covering the entire area at a single density. Results from this experiment are applied to understand simulation outcomes in part 2 of the series.

Technical Abstract: We propose a novel, “core-and-perimeter” (C&P) delimiting trapping survey design for invasive insects, which could be more resource efficient and effective than the ubiquitous fully trapped (FT) square grids using regular spacing. The C&P design only has traps near the epicenter and in a perimeter set at a distance to result in zero captures, thereby effectively setting the boundary of an incursion. We compared the C&P and FT designs in a mark-release-recapture experiment with Ceratitis capitata (Wiedemann) in Hawaii, with eight total repetitions in 2022. The square FT grid had 99 traps over 0.92-km2, plus 24 “sentinel” traps just outside. The circular C&P grid had 20 core traps, and 108 traps in a 220 m-wide perimeter, set 500 m from the release point. That was smaller than the recommended radius, to fit the setting. Every repetition had four releases of flies, and six collection days from 1 to 14 days after release. The C&P design had greater kernel-smoothed density near the edges, while the FT design was more uniform, as expected. More flies on average were captured in the FT treatment, but this difference was not statistically significant, and proportional captures in common locations were also not significantly different (a = 0.05). Flies were caught in the sentinel traps in every replicate of the FT treatment, demonstrating the potential for undetected egress from the trapping grid. In the C&P treatment, four percent of captures were in the perimeter on average. The trap usage rate for the core area of the C&P design was nearly 94 percent, whereas the same rate for the whole FT design was only 67 percent. Mean daily dispersal distance was 96.3 m over both treatments, and a combined regression over treatments for total distance gave a 99th percentile of about 700 m, and a 99.99th percentile of 949.6 m. This matched other empirical studies of C. capitata dispersal. The results demonstrated two FT design flaws—trap inefficiency and egress potential—and the potential effectiveness of the C&P design. These empirical data will be used to build a dispersal simulation mode to evaluate the C&P design more fully.