Using delimiting surveys to characterize the spatiotemporal dynamics facilitates the management of an invasive non-native insect

The ability to ascertain abundance and spatial extent of a nascent population of a non-native species can inform management decisions. Following initial detection, delimiting surveys, which involve the use of a finer network of samples around the focal point of a newly detected colony, are often used to quantify colony size, spatial extent, and the location of the population core. Despite the widespread use of pheromone-baited traps in delimitation surveys to manage invading populations of Lymantria dispar (L.) in North America, there has been no prior comprehensive attempt to analytically determine the adequacy of these surveys. We used data from 2,190 delimiting grids collected from 2000 to 2010 in the United States to quantify the information gained from delimiting surveys. The use of delimiting surveys revealed that ≈53 % of populations of low initial abundance persisted as detectable populations in the following year; however, when trap data from delimiting surveys were excluded, only ≈16 % of these low density populations were detected in the following year. Measurements of abundance and spatial extent of a detected population were affected by the increased use of delimiting traps after accounting for initial abundance, the distance from an infested area, and colony area. The use of delimiting traps had a lesser effect on the estimation of the spatial location of the population core, indicating that initial detection of a population often reflects the population core. The need to prioritize resources in efforts to manage non-native species is paramount, and early detection is a key in invasive species management.