Choice behaviour and performance of Cassida stigmatica on various chemotypes of Tanacetum vulgare and implications for biocontrol

Abstract

Biological control is often an effective technique deployed to tackle invasive plant species by the release of highly specialized enemies. However, variation in plant chemistry due to high plasticity and/or evolved during the introduction process needs to be considered when testing the efficacy of potential biocontrol agents. The tortoise beetle, Cassida stigmatica Suffrian (Coleoptera: Chrysomelidae), is a potential biological control agent selected to control the chemically highly variable and invasive plant species Tanacetum vulgare L. (Asteraceae). This study was conducted to test whether or not plants of different chemical profiles (terpene chemotypes) are equally accepted by C. stigmatica. Therefore, female oviposition and feeding choice behaviour were examined using one pure chemotype (β-thujone type) and three mixed chemotypes (camphor/1,8-cineole, β-thujone/camphor, and camphor/camphene types) in various paired-choice combinations. Furthermore, larval survival and adult body mass were compared when beetles were reared on the four chemotypes. Overall, C. stigmatica females showed a clear preference for the pure β-thujone chemotype over the mixed chemotypes containing camphor, and no preferences when only mixed chemotypes were offered in choice tests. However, they were able to use all offered chemotypes for oviposition and feeding. No differences in larval survival and adult body mass could be detected when reared on the various chemotypes. The study demonstrates that knowledge of the acceptance of chemically variable host species is essential when testing for applicability of biocontrol agents.