Chemodiversity in flowers of Tanacetum vulgare has 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 insects. Tanacetum vulgare plants vary significantly in their leaf terpenoid composition, forming distinct chemotypes. We investigated the composition of terpenoids and nutrients 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) – using different analytical platforms. 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 the above chemotypes, while total concentrations of pollen terpenoids, sugars, amino acids, and lipids did not differ. Beetles preferred BThu over the Myrox chemotype in both olfactory and contact choice assays, while the Keto chemotype was marginally repellent according to 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 when feeding 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.

Flower visitor groups show differential responses to individual and plot-level chemodiversity with consequences for plant fitness

“…The flower heads showed the same chemotype as the leaves in our field-grown plants, as previously also found for T. vulgare plants grown under a controlled greenhouse environment (Sasidharan et al, 2023). Thus, in this species the chemotype, defined here by one to three dominant terpenoids, is a unique phenotype of the individuals’ aboveground organs and consistent under different conditions (Kleine and Müller, 2011, Benedek et al, 2015, Ziaja and Müller, 2023).…”

“…(Table 1), which are specialists on Asteraceae (Gaafar et al, 2016). Preferences for certain chemotypes were also found in laboratory studies for Olibrus aeneus , which preferred the BThu over the Myrox chemotype in olfactometer and contact dual choice assays (Sasidharan et al, 2023). In the field, preferences may be related to different abundances of certain chemotypes (Bálint et al, 2016, Bustos-Segura et al, 2015, Humay et al, 2023) and depend on local adaptations of insect populations (Laukkanen et al, 2012, Kalske et al, 2016).…”

“…According to the interaction diversity hypothesis, chemodiversity arises from interactions with a diverse community in terms of both species and their functional roles (Kessler and Kalske, 2018, Wetzel and Whitehead, 2020). Within plants, particularly flowers engage with animals of various functional groups, aiming to attract beneficial pollinators and deter floral herbivores, known as florivores (Raguso, 2016, Sasidharan et al, 2023, Schiestl, 2015). High chemodiversity may serve these different purposes.…”

“…While some specialised metabolites attract pollinators, others could repel them, resulting in selective pollination and specialisation in plant-pollinator relationships (Raguso, 2008). Florivores are likewise attracted or repelled by different flower chemicals and can show preferences to specific chemotypes (Knudsen and Gershenzon, 2006, Sasidharan et al, 2023, Schiestl, 2015). Some plants avoid trade-offs between the simultaneous attraction of pollinators and florivores by modulating specialised metabolite or reward production (Kessler et al, 2013, Theis et al, 2007) or by deploying herbivore-specific repellents (Raguso, 2016).…”

“…Tanacetum vulgare L., common tansy (Asteraceae), is a perennial plant that exhibits remarkable chemodiversity in its leaf and floral terpenoid composition, forming distinct chemotypes (Keskitalo et al, 2001, Kleine and Müller, 2011). Various insects exhibited differential attraction to and/or growth performance on these chemotypes, including leaf-feeders (Ojeda-Prieto et al, 2023, Wolf et al, 2012, Ziaja and Müller, 2023) and florivores (Eilers et al, 2021, Sasidharan et al, 2023). Moreover, previous studies suggest that leaf and flower herbivores respond differently to individual chemotypes compared to the heterogeneity of chemotypes in the neighbourhood (Eilers et al, 2021, Ziaja and Müller, 2023).…”