Occurrence patterns of aspen‐feeding wood‐borers (Coleoptera: Cerambycidae) along the wood decay gradient: active selection for specific host types or neutral mechanisms?

1. Determinants of host‐use patterns in plant‐feeding insects have been extensively studied, usually within the framework of optimality theory. Comparatively, factors driving host selection in saprophagous insects have received little attention. 2. In this study, mechanisms creating occurrence peaks of saprophagous wood‐borers (Cerambycidae: Coleoptera) in standing dead aspen in the middle and late stages of decay were investigated by correlating insect occurrence with variations in substrate‐related nutritional and physical parameters. Twenty‐four snags at four decay stages were dissected from a mature stand in western Quebec, Canada. Wood samples were taken to measure levels of nitrogen, non‐structural carbohydrates, phenols, wood density, water content and snag age. 3. Several nutritional and physical parameters varied significantly along the decay gradient and were correlated with insect occurrence, but all significant parameters were also strongly correlated with snag age and wood density. Model selection using Akaike’s second order information criteria was used to rank the different models; the model including snag age only performed best, with a w i of 0.873. 4. This importance of snag age gives support to a proposed hypothesis of host selection in which temporal autocorrelation in probability of insect occurrence explains peaks observed in the middle and late stages of decay. However, further studies will be needed to confirm the prevalence of such neutral mechanisms over active selection in the determination of host‐use patterns in decaying aspen.