Physical characteristics as potential host selection cues for Leptoglossus occidentalis (Heteroptera: Coreidae)

Abstract

Leptoglossus occidentalis Heidemann exhibits pronounced clonal host preferences throughout seed orchards in British Columbia. We investigated the hypothesis that these preferences could result in part from perception of physical characteristics of the host trees. Surveys were conducted in 2 Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, and 2 lodgepole pine, Pinus contorta variety latifolia Engelmann, seed orchards over a 3-yr period. Tree height, cone density, and flowering phenology data were obtained for each tree surveyed. Chi-square analyses disclosed significant discrepancies between the frequency distributions of trees selected by L. occidentalis and the frequency distributions of trees by height class, cone density class, and particularly height and cone density classes Combined. Seed bugs avoided short trees with low cone density, but also avoided the tallest trees with the greatest cone density. Because trees with moderate numbers of cones tend to have large cones with many seeds per cone, it would be highly adaptive for seed bugs to select such trees. Visual reflectance measurements demonstrated that conelets consistently reflected more light and at different wavelengths than foliage. Conelets from preferred clones reflected more light over a broader range of wavelengths than those from nonpreferred clones. A hypothetical decision tree model was developed incorporating 4 key steps that may be used by L. occidentalis to select host trees.