Soil amendment with insect frass and exuviae affects rhizosphere bacterial community, shoot growth and carbon/nitrogen ratio of a brassicaceous plant

Abstract

Aims In terrestrial ecosystems, deposition of insect frass and cadavers in the soil influences soil characteristics, including microbial community composition, with consequences for plant growth and development. Insect frass and exuviae are also a major residual stream from insect production for food and feed, that may be used as soil amendment. However, only few studies have thoroughly examined the effect of soil amendment with insect frass and exuviae on rhizosphere microbial communities and plant growth. Methods We studied the effects of soil amendment with frass and/or exuviae originating from three insect species, Tenebrio molitor, Acheta domesticus, and Hermetia illucens, at three different concentrations, compared to synthetic fertiliser. At several time points we analysed the rhizosphere bacterial community and assessed multiple plant-growth parameters of a brassicaceous plant. Results Soil amendment with frass and/or exuviae improved plant growth at least as well as synthetic fertiliser, A. domesticus exuviae having the strongest impact. The origin (insect species), type (frass or exuviae) and concentration of soil amendment influenced the effects on plant traits. The rhizosphere bacterial community differed between amended and unamended soil. Bacterial genera that contain plant growth-promoting species were more abundant in the rhizosphere of plants grown in amended soil. Conclusions Addition of insect frass and/or exuviae to the soil differentially affects the bacterial rhizosphere community and promotes plant growth in these soils, underlining their unique roles in the aboveground-belowground feedback loop, and their potential use as soil amendment in circular agriculture.

Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae

“…However, soil amendment with purified chitin in a similar concentration as was added with the exuviae amendments, did not lead to an increase in shoot dry biomass of B. oleracea in the field. These results support the hypothesis that the effects of insect exuviae on plant growth are not strongly dependent on chitin content (Van de Zande et al., 2023; Wantulla et al., 2023).…”

“…However, soil amendment with black soldier fly exuviae led to an increased visitation by pollinators of Brassica nigra plants in the field (Barragán‐Fonseca et al., 2023). Furthermore, soil amendment with insect exuviae selectively stimulated the relative abundance of several rhizosphere bacterial genera that include PGPR species (Van de Zande et al., 2023; Wantulla et al., 2023). Inoculation with PGPR may increase plant headspace volatile emission (Rasmann et al., 2017).…”

“…The raw data are publicly available from 4TU.ResearchData via https://doi.org/10.4121/d5fdbc3e-396c-465c-9807-76f468bed6df (Van de Zande et al., 2024).…”

“…Moreover, soil amendment with insect residues such as frass or exuviae increased soil nitrogen availability up to 16 weeks after amendment (Nurfikari et al., 2023). Furthermore, soil amendment with insect residues increases the relative abundance of bacterial genera in the rhizosphere that include plant growth‐promoting rhizobacteria (PGPR) (Van de Zande et al., 2023; Wantulla et al., 2023) and resulted in larger plants with a lower carbon/nitrogen ratio (Van de Zande et al., 2023). Whether soil amendment with insect residues affects the emission of HIPV upon herbivore damage remains to be investigated.…”

Lactic Acid Bacteria from Bombyx mori Frass: Probiotic Properties and Antagonistic Activities

“…This waste material represents a significant by-product of silkworm rearing and is produced in large quantities in Southeast Asian countries, including Thailand. Silkworm faeces, rich in (plant) nutrients and mixed with undigested substrate residues (frass), are used as organic fertilisers and in biogas production [9][10][11]. In Thailand, silkworm frass serves as a vital fertiliser for mulberry plantations, offering organic nutrients and showcasing sustainable agricultural practices.…”