Simulation-based investigation of the performance of delimiting trapping surveys for insect pests

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

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2021
Publication Date: 10/11/2021
Citation: Caton, B.P., Fang, H., Manoukis, N., Pallipparambil, G.R. 2021. Simulation-based investigation of the performance of delimiting trapping surveys for insect pests. Journal of Economic Entomology. 114(6):2581–2590. https://doi.org/10.1093/jee/toab184.
DOI: https://doi.org/10.1093/jee/toab184

Interpretive Summary: Following detection of an invasive pest, response agencies often conduct a process called "delimitation". This entails setting up a large number of traps (a grid) to 1) confirm presence of the pest and 2) determine how far it has spread. This study uses a computer model to test possible improvements to the standard delimiation trap placement approach by considering insect movement, grid size and shape, trap attraction, and number of traps per unit area. Possible improvements to grid design that would realize cost savings while maintaining delimiation goals are proposed.

Technical Abstract: Fully trapped survey designs are widely used to delimit adventive pests populations that can be detected using traps and lures. Delimitation includes verifying the presence of the pest and determining its spatial extent. The size and shape of the survey design and the density of traps can vary; however, resulting variation in detecting efficiency is often unknown. We used a trapping network simulation model with diffusion-based insect,movement to investigate delimiting survey trapping design performance for fully trapped and some modified designs. Simulations included randomized outbreak locations in a core area, and a duration of 30 days. We assessed impacts of insect dispersal ability, grid size and shape, and trap attractiveness and density on survey performance, measured as mean probability of capturing individual pests [p(capture)]. Most published grids are square, but circles performed equally well and are more efficient. Over different grid sizes, p(capture) increased for insects with greater dispersal ability but was generally unresponsive to size because most captures occurred in central areas. For low dispersing insects, the likelihood of egress was approximately zero with a 3.2-km square grid, while a 11.3-km grid was needed to contain highly vagile insects. Trap attractiveness affected (capture) more strongly than density: lower densities of poorly attractive traps may underperform expectations. Variable density designs demonstrated potential for cost savings but highlighted that resource-intensive outer bands are critical to boundary determination. Results suggesting that many grids are oversized need empirical verification, while other principles, such as using circular shapes, are readily adoptable now.