Chemodiversity in flowers ofTanacetum vulgarehas consequences on a florivorous beetle

Abstract

The chemical composition of plant individuals can vary, leading to high intraspecific chemodiversity. Diversity of floral chemistry may impact the responses of flower-feeding insect visitors. Plants of Tanacetum vulgare vary significantly in their leaf terpenoid composition, resulting in distinct chemotypes. We investigated the composition of terpenoids and nutritents of flower heads and pollen in plants belonging to three chemotypes, dominated either by β-thujone (BThu), artemisia ketone (Keto) or a mixture of (Z)-myroxide, santolina triene and artemisyl acetate (Myrox). Moreover, we tested the effects of these differences on preferences, weight gain and performance of adults of the shining flower beetle, Olibrus aeneus. The terpenoid composition and diversity of flower heads and pollen significantly differed among individuals belonging to these chemotypes, while total concentrations of terpenoids, sugars, amino acids or lipids of the pollen did not differ. Beetles preferred the BThu over the Myrox chemotype in both olfactory and contact choice assays, while the Keto chemotype was marginally repellent in olfactory assays. The beetles gained the least weight within 48 h and their initial mortality was highest when feeding exclusively on floral tissues of the Myrox chemotype. Short-term weight gain and long-term performance were highest on the BThu chemotype. In conclusion, the beetles showed chemotype-specific responses towards different T. vulgare chemotypes, which may be attributed to the terpenoid composition in flower heads and pollen rather than to differences in nutrient profiles. Both richness and overall diversity are important factors when determining chemodiversity of individual plants and their consequences on interacting insects.