Summary1. Community structure involving large taxonomical groups is frequently used to assess changes in ecosystems along environmental gradients or in response to disturbance. For terrestrial arthropods, abundance is generally used as the response variable in community data analyses; biomass, however, is generally a better indicator of the functionality of a species within a community, as it is strongly correlated with metabolism. 2. In this study, we considered whether biomass should be used more often in community analyses with terrestrial arthropod biodiversity data, particularly when asking questions involving strong functional components. We selected 10 previously published and five unpublished Coleoptera abundance data sets, and produced biomass species-by-sample matrices using body length to body mass conversion equations, and then compared the results obtained using commonly used ecological analyses. 3. Correlations between species abundance and biomass varied from strong to poor, depending on the taxa considered and on the sampling method used. We show that abundance and biomass can produce different results in community data analysis and lead to alternative interpretations for data sets with poor abundance to biomass correlations. 4. Synthesis and applications . When dealing with databases showing poor abundance to biomass relationships, the question of the relevance of using biomass instead of abundance emerges, and the choice of the response variable to be used in analyses should be considered carefully. At the very least, when studying terrestrial arthropod biodiversity, one should consider the use of biomass with simple conversion equations that do not require obtaining the mass of individual specimens. This approach may lead to different interpretations. For research questions in which trophic interactions may play an important role, biomass may provide a broader and more accurate picture of the processes driving changes in community structure.

1 Most plant-feeding insects show some degree of specialization and use a variety of cues to locate their host. Two main mechanisms of host location, primary attraction and random landing, have been investigated for such insects. 2 Research has led to contradictory conclusions about those hypotheses, especially for wood-feeding insects; however, recent studies suggest that both mechanisms may take place in a single taxon but at different scales. 3 We developed a field experiment to test the hypothesis that primary attraction occurs at larger scale and random landing at finer scale in wood-feeding insects.Landing rates, measured using sticky traps, were compared first between patches and then between individual trees according to their distance to a baited central tree. 4 Polynomial functions describing landing rate to distance relationships were compared with a function produced by a null model describing what should occur under the random landing hypothesis. Scolytidae and Cerambycidae (Coleoptera) responded to volatiles at the patch scale, supporting the primary attraction hypothesis, but the landing patterns of some groups at finer scale matched closely the predictions of our null model, giving support to the random landing hypothesis. 5 Our results show that the primary attraction and random landing hypotheses are not mutually exclusive and that prelanding use of host-produced volatile is scaledependant. Scale considerations should thus be included in the study of prelanding host-selection of wood-feeding insects.

Wood‐feeding insects play important functional roles in forest ecosystems, contributing significantly to wood decay processes. However, sampling these species in a direct and quantitative way is difficult because they live most of their lives as larvae deep into the wood; knowledge of species‐specific host‐use patterns along the decay gradient is thus lacking in this group. To cope with these difficulties, we used a novel approach, snag dissection, to investigate occurrence patterns of such Coleoptera adults and larvae. We selected 80 snags of both black spruce and aspen along four classes of decay in five different stands distributed over the tree species’ ranges within the province of Quebec, Canada, and dissected a one‐meter section of each. All adults and larvae of Buprestidae, Cerambycidae and Scolytinae (Coleoptera: Curculionidae) were collected and identified to the lowest taxonomical level possible. Wood density and snag age were also calculated for each sampled snag. In black spruce, host‐use was mostly concentrated at the beginning of the decay gradient. Patterns observed in aspen were opposite, as few insects were found in fresh snags, while most snags in middle to late stages of decay contained insects, often in large numbers, in some reaching densities of over 1000 cerambycid larvae m−3. For both tree species, patterns observed were similar across regions sampled. Differences in host‐use patterns between the coniferous and deciduous host species may be due to differences in secondary chemistry, mechanical defence mechanisms or the stand dynamics typically associated with each tree species.