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Research article2023Peer reviewedOpen access

Impact across ecosystem boundaries-Does Bti application change quality and composition of the diet of riparian spiders?

Kolbenschlag, Sara; Bollinger, Eric; Gerstle, Verena; Bruehl, Carsten A.; Entling, Martin H.; Schulz, Ralf; Bundschuh, Mirco

Abstract

Emerging aquatic insects link aquatic and adjacent terrestrial food webs by subsidizing terrestrial predators with high -quality prey. One of the main constituents of aquatic subsidy, the non-biting midges (Chironomidae), showed altered emergence dynamics in response to the mosquito control agent Bacillus thuringiensis var. israelensis (Bti). As riparian spi-ders depend on aquatic subsidy, they may be affected by such changes in prey availability. Thus, we conducted a field study in twelve floodplain pond mesocosms (FPMs), six were treated with Bti (2.88 x 109 ITU/ha, VectoBac WDG) three times, to investigate if the Bti-induced shift in chironomid emergence dynamics is reflected in their nutritional value and in the diet of riparian spiders. We measured the content of proteins, lipids, glycogen, and carbohydrates in emerged Chironomidae, and determined the stable isotope ratios of female Tetragnatha extensa, a web-building spi-der living in the riparian vegetation of the FPMs. We analysed the proportion of aquatic prey in spiders' diet, niche size, and trophic position. While the content of nutrients and thus the prey quality was not significantly altered by Bti, ef-fects on the spiders' diet were observed. The trophic position of T. extensa from Bti-treated FPMs was lower compared to the control while the aquatic proportion was only minimally reduced. We assume that spiders fed more on terrestrial prey but also on other aquatic organisms such as Baetidae, whose emergence was unaffected by Bti. In contrast to the partly predaceous Chironomidae, consumption of aquatic and terrestrial primary consumers potentially explains the observed lower trophic position of spiders from Bti-treated FPMs. As prey organisms vary in their quality the suggested dietary shift could transfer previously observed effects of Bti to riparian spiders conceivably affecting their populations. Our results further support that anthropogenic stressors in aquatic ecosystems may translate to terrestrial predators through aquatic subsidy.

Keywords

Chironomidae; Tetragnatha extensa; Stable isotope analysis; Nutrient content; Bacillus thuringiensis var; israelensis; Aquatic -terrestrial linkage

Published in

Science of the Total Environment
2023, Volume: 873, article number: 162351Publisher: ELSEVIER

    Sustainable Development Goals

    SDG15 Life on land

    UKÄ Subject classification

    Ecology
    Environmental Sciences

    Publication identifier

    DOI: https://doi.org/10.1016/j.scitotenv.2023.162351

    Permanent link to this page (URI)

    https://res.slu.se/id/publ/121825