Fungicide treatments drive changes in the diversity and species richness of tissue-resident bacteria in agrobiont cobweb-weaving and epigeic spiders

Abstract

Agrochemicals have the potential to induce large-scale changes in the abundance and diversity of endosymbionts. Moreover, although there is still no direct proof of the ability of Rickettsia and Wolbachia to degrade or detoxify insecticides or other agrochemicals, changes in the abundance or diversity of endosymbiotic bacteria were reported to alter insecticide resistance. We hypothesized that treatment with one or more fungicides affects the species richness and relative abundance of microbial endosymbionts of agrobiont cobweb-weaving and epigeic spiders. We further hypothesized that microbial endosymbiont composition may affect agrochemical resistance. We used Phylloneta impressa as a model cobweb-weaving species and Pardosa agrestis as a model epigeic species and tested the effects of four chemically unrelated fungicides, Captan, Kocide (copper oxychloride), Kuprikol (copper hydroxide), and Super Tin (triphenyltin hydroxide). Furthermore, we determined the resistance to three other agrochemicals, Benevia (cyantraniliprole), Coragen (chlorantraniliprole), and Mospilan (acetamiprid). The analyses were based on 16S rDNA profiles from lysates of the cephalothorax and legs of the tested spiders. Fungicide treatment induced prominent changes in the diversity and richness of tissue-resident bacterial assemblages, including facultative and obligate endosymbionts. However, the direction of the observed responses varied with the fungicide used and differed between the two tested species. The observed fungicide-induced changes had direct effects on resistance to insecticides. Namely, Captan treatment and/or altered diversity and richness of facultative and obligate endosymbionts led to increases in Benevia (cyantraniliprole) resistance of the host spiders. The combined data show that fungicides shape the tissue-associated bacterial communities in spiders, including their endosymbionts. Both study species had a high prevalence of infection of Rickettsia and Wolbachia and a 100 % prevalence of Spiroplasma. These endosymbiotic genera responded to the fungicide treatment, and changes in their relative abundance were associated with the possible onset of Benevia (cyantraniliprole) resistance.