ABUNDANCE, SPECIES RICHNESS, HOST UTILIZATION AND HOST SPECIFICITY OF INSECT FOLIVORES FROM A WOODLAND SITE, WITH PARTICULAR REFERENCE TO HOST ARCHITECTURE

We studied the local abundance, species richness, host utilization and host specificity of insect folivores associated with 10 deciduous woody and 10 perennial herbaceous plant species growing in a woodland site in the Swiss Jura. Regional species richness of insect folivores on their hosts, inferred from compilation of insect faunas for Central Europe, was highly correlated with local species richness, as estimated by a 7-month field survey. Woody hosts sustained more insect species and a higher proportion of chewers, than herbaceous plants which, in turn, sustained a higher proportion of leaf miners. Overall insect abundance was not affected by plant architecture. On average, 56 % of the species feeding upon a particular host were specialists, with no apparent effect of plant architecture, but proportions for herbaceous plants fluctuated from 0 to 100 %. At the regional scale, 85 % of the variance in herbivore species richness was explained by the height of the host, its taxonomic relatedness and its leaf water content. At the local scale, 88 % of the variance could be explained, with a significant contribution of host phenology. The variances explained by models describing other local variables - such as herbivore abundance, number of specialist species, proportions of ectophagous/endophagous species and leaf palatability - were generally lower, with, sometimes, a significant contribution of sampling effort. Although confirmation will be needed from more extensive studies, particularly encompassing plants growing in other habitats, we suggest that the influence of variables such as leaf water and host phenology may have been underestimated as predictors of herbivore species richness.