Maximizing information yield from pheromone-baited monitoring traps: Estimating plume reach, trapping radius, and absolute density of randomly moving insects

Monitoring traps perform very well for recording what insect pests are present in a crop and when they are active. However, translating catch numbers into actual pest numbers per area has, until now, rarely been accomplished. This dissertation reveals how novel methods of data analysis were used to interpret catch data from both single-trap, multiple-release and single-release to a 5 x 5 trapping grid experiments using two model organisms, codling moth (Cydia pomonella) and Japanese beetle (Popillia japonica) responding to standard pheromone baited and floral plus pheromone baited traps, respectively. The main objectives were to produce reliable measurements of: 1) the attractant plume reach from the trap, 2) the maximum dispersive distance of a population of responders, 3) the proportion of the population in the trapping area caught (Tfer), and 4) the patterns of movement (C.S.D.). Two release designs were employed for codling moth: 1) releases in the four cardinal directions, and 2) even releases across 16 ha orchard blocks using both high and low CM populations. For both release designs at high populations, the unadjusted mean proportion caught (Tfer) was 0.01 as compared to 0.02 for even releases of low populations. Mean maximum dispersive distance for released codling moth males was ca. 260 m. Plume reach for the standard CM trap was only ca. 2 m, total trapping area for a single trap was ca. 21 ha., and the measure of meander of 37°. These estimates were consistent across three growing seasons and are supported by extraordinarily high replication for this type of field experiment. For Japanese beetle a foraging meander of 9 +/- 3° C.S.D. was revealed and the plume reach from the Trece Catch Can trap baited with the dual baitpack lure was 10 m. Measures of Tfer and maximum dispersive distance of 0.06 and 120 m per day were measured. Knowing the trapping area and the Tfer values for these model insects permits catch numbers from single monitoring traps to be translated into absolute pest density using the equation: males per trapping area = catch per trapping area / Tfer . Finally, the mean of 5 traps spaced one tree apart produced considerably more precise measures of absolute codling moth density than did a single trap. This fundamental knowledge of how to space traps and interpret catch numbers will enable pest mangers to make considerably more precise projections of damage and therefore more precise and reliable decisions on whether insecticide applications are justified. The principles and methods established here for estimating absolute insect density should be broadly applicable and thereby set a new standard for IPM decisions based on trapping.