Assessment of cues potentially mediating host selection of Leptoglossus occidentalis on Pinus contorta

Leptoglossus occidentalis causes significant damage in conifer seed orchards. Host selection by L. occidentalis is not completely understood. Earlier research has demonstrated a preference for certain clones of Pinus contorta, indicating that L. occidentalis responds to chemical or physical cues. The present study aimed to test whether L. occidentalis shows clonal preference across years, and to examine whether the host cues responsible for this could be identified. Surveys were conducted in a lodgepole pine seed orchard in British Columbia in 2008 and 2009. Clones were ranked based on the proportion of their ramets on which L. occidentalis was observed. Ramets were divided into three classes: (i) preferred clones with seed bugs; (ii) preferred clones without seed bugs; and (iii) nonpreferred clones with zero or very low numbers of seed bugs. From each clone, we measured infrared radiation emitted from cones, cone monoterpenes, cone size and numbers of cones per tree. Clone preference was consistent between 2008 and 2009. Clone preference classes differed significantly in α-pinene and δ-3 carene and limonene. Leptoglossus occidentalis was found more frequently on clones with cones of greater diameter and weight. Infrared radiation did not differ between clone preference classes, indicating that it is not used in host acceptance.