THE IMPORTANCE OF NEEDLE TERPENE COMPOSITION IN DETERMINING THE MACROLEPIDOPTERA SPECIES RICHNESS OF CANADIAN CONIFERS

The effect of host-plant biochemical relatedness (using needle terpene data) in explaining the variation in macrolepidoptera species richnes s of Canadian conifers was investigated. Conifer geographic range acco unted for 25-35% of the variance in species richness. A total of 61% o f species richness variance was explained by adding tree height as a v ariable. Taxonomic relatedness (number of species per genus) did not e xplain a significant amount of variance. Five measures of biochemical relatedness were calculated, including number of terpenes and similari ty/dissimilarity indices using presence and absence as well as abundan ce of individual terpenes. Individually, three measures of biochemical relatedness explained a similar amount of variance in species richnes s as conifer geographic range. When entered in stepwise multiple regre ssion equations, only about 8% extra variance was explained by these i ndices. One measure, however, entered first and alone accounted for 31 % of the variance. Measures of biochemical relatedness were the only v ariables that significantly accounted for Variance in the similarity o f macrolepidoptera faunas from different conifers.Species from the Cup ressaceae were more biochemically dissimilar to the rest of the specie s in the sample than species from the Pinaceae. When regression analys is considered only the Pinaceae no measure of biochemical relatedness explained a significant amount of variance in species richness. I conc lude that conifer needle terpene composition is important in determini ng interfamily differences in macrolepidoptera species richness, but t hat at the intra-family level this is insensitive to plant secondary c hemistry.