1 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. 2 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. 3 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. 4 Clone preference was consistent between 2008 and 2009. Clone preference classes differed significantly in -pinene and -3 carene and limonene. 5 Leptoglossus occidentalis was found more frequently on clones with cones of greater diameter and weight. 6 Infrared radiation did not differ between clone preference classes, indicating that it is not used in host acceptance.

We tested the hypothesis that the conophagous Douglas-fir cone gall midge, Contarinia oregonensis Foote (Diptera: Cecidomyiidae), responds to infrared (IR) radiation and other electromagnetic wavelengths associated with cones of Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco (Pinaceae). Early-season (March–April) thermographic images showed that cone orientation (upright, horizontal, pendant) and cone colour (green, purple, green/purple) did not affect apparent cone temperature (inferred from thermographic images). Tree components significantly differed in apparent temperature with foliage being coolest and branches warmest. There was no significant difference in the number of larvae in cones of different colours, and adult midges were equally attracted to traps painted green or purple, suggesting that cone colour does not affect oviposition decisions by gravid females. Adult midges were more strongly attracted to warm traps with IR frequency emissions higher than the background than to cold traps with IR frequency emissions lower than the background. They were also more strongly attracted to warm branch-shaped traps than to warm can-shaped traps. Collectively, these data indicate that the shape and IR attributes of Douglas-fir branches may serve as foraging cues for C. oregonensis.