title: How generalist herbivores exploit belowground plant diversity in temperate grasslands.
abstract: Belowground herbivores impact plant performance, thereby inducing changes in plant community composition, which potentially leads to cascading effects onto higher trophic levels and ecosystem processes and productivity. Among soil-living insects, external root-chewing generalist herbivores have the strongest impact on plants. However, the lack of knowledge on their feeding behaviour under field conditions considerably hampers achieving a comprehensive understanding of how they affect plant communities. Here, we address this gap of knowledge by investigating the feeding behaviour of Agriotes click beetle larvae, which are common generalist external root-chewers in temperate grassland soils. Utilizing diagnostic multiplex PCR to assess the larval diet, we examined the seasonal patterns in feeding activity, putative preferences for specific plant taxa, and whether species identity and larval instar affect food choices of the herbivores. Contrary to our hypothesis, most of the larvae were feeding-active throughout the entire vegetation period, indicating that the grassland plants are subjected to constant belowground feeding pressure. Feeding was selective, with members of Plantaginaceae and Asteraceae being preferred; Apiaceae were avoided. Poaceae, although assumed to be most preferred, had an intermediate position. The food preferences exhibited seasonal changes, indicating a fluctuation in plant traits important for wireworm feeding choice. Species- and instar-specific differences in dietary choice of the Agriotes larvae were small, suggesting that species and larval instars occupy the same trophic niche. According to the current findings, the food choice of these larvae is primarily driven by plant identity, exhibiting seasonal changes. This needs to be considered when analysing soil herbivore-plant interactions.
authors.affiliation: Mountain Agriculture Research Unit, Institute of Ecology, University of Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria.
authors.forename: Corinna
authors.initials: C
authors.lastname: Wallinger
authors.forename: Karin
authors.initials: K
authors.lastname: Staudacher
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Schallhart
authors.forename: Evi
authors.initials: E
authors.lastname: Mitterrutzner
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Steiner
authors.forename: Anita
authors.initials: A
authors.lastname: Juen
authors.forename: Michael
authors.initials: M
authors.lastname: Traugott
mesh_terms: D000818:Animals; D044822:Biodiversity; D001517:Coleoptera / Q000502:physiology*; D004247:DNA / Q000032:analysis; D004032:Diet; D005247:Feeding Behavior; D020387:Food Chain; D060434:Herbivory; D007814:Larva / Q000502:physiology; D018517:Plant Roots; D006109:Poaceae; D012621:Seasons; D017422:Sequence Analysis, DNA
chemical_list: D004247:DNA
keywords: Agriotes obscurus; Agriotes sputator; root feeding; soil herbivory; trophic interaction