Too close for comfort: effect of trap spacing distance and pattern on statistical inference of behavioral choice tests in the field

Abstract

AbstractBehavioral choice tests provide a powerful and commonly used technique for evaluating the biological activity of chemical signals. Despite the widespread application of this approach, relatively few studies have evaluated a key assumption, that is, relative independence among treatments. Previous work has demonstrated that both the number of choices and their physical arrangement can affect the results of choice tests with leaf‐feeding insects in laboratory assays. Here, we consider another spatial component, the distance between treatments, in a field assay, using a bark beetle as our model. We used three geometries of trap arrangements, two spacing levels, and both ‘low activity’ lures and a ‘high activity’ lure in our behavioral assays. We found that proximity to an attractive treatment generated unexpectedly high trap catches at relatively non‐attractive treatments, even in the presence of a uniform treatment effect and relatively constant insect population size. Increases in traps baited with ‘low activity’ lures proximate to a highly attractive treatment ranged from 4 to 7× the catch observed in configurations with traps spaced wider apart. Moreover, even in the absence of ‘high activity’ lures, a lure catching less than one insect per day on average could obscure the effect of a control trap at proximate spacing. In our example, a spacing distance of 15 m appears to provide independence among traps used to sample the bark beetle Ips pini (Say) (Coleoptera: Curculionidae: Scolytinae), but 3 m does not. Our broader intent is to provide a useful approach to the design and evaluation of behavioral choice experiments in the field.