Estimating Pathways of Migrating Insects Carried in Atmospheric Winds1

Abstract

A numerical trajectory analysis scheme is used to estimate the pathways of insects in the lowest 2 km of the atmosphere during three hypothetical pest migrations. The investigation incorporated winds-aloft data from a series of special meteorological field experiments conducted over the eastern United States during the spring of 1979. Hypothetical pest-catch sites were chosen from which trajectories were constructed upwind (back-trajectories) at seven levels between the surface and 800 mb (ca. 2,000 m). Comparisions were made between 12-h data (the normal operational interval) interpolated to 3 hand 3-h observed data to examine temporal variabilities in the near-surface wind fields. In addition, back-trajectories were constructed with data using only the regular upper air sounding network versus the regular network supplemented with additional sites to explore differences due to increases in the horizontal resolution of the wind. Finally, an intercomparsion study was conducted with several trajectory analysis methods of pest migration studies reported in the literature and the objective procedure described here. Results suggest that increased resolution of the vertical structure of the horizontal wind fields substantially decreases the uncertainties in the estimated paths of migrants. Increases in the temporal and horizontal frequencies of the wind produced differences in back-trajectory endpoints that were 4–5 times smaller than those from the improved vertical resolution. Backtracking methods of previous researchers appeared to provide reasonable approximations of potential source regions for migrants, but only when both surface and upper air data were incorporated into the analysis and with lower-tropospheric airflow conditions that were reasonably homogeneous.