Soil amendment with insect exuviae causes species-specific changes in the rhizosphere bacterial community of cabbage plants

Insect exuviae are a chitin-rich by-product of insect farming that is considered to have great potential for contributing to sustainable agriculture. When used as soil amendment, insect exuviae have been suggested to promote plant growth and health by stimulating naturally occurring beneficial microbes. In a greenhouse experiment, the exuviae of black soldier fly larvae (Hermetia illucens L.), house crickets (Acheta domesticus L.), and yellow mealworms (Tenebrio molitor L.) were added to soil from an organically managed field. Brussels sprouts, Brassica oleracea L., plants were grown in amended soil to assess effects on plant growth and investigate bacterial abundance, diversity, and community composition in the rhizosphere. All soil amendments increased plant shoot biomass and stimulated bacterial growth. At the same time, bacterial diversity was diminished and the different amendments resulted in distinct bacterial communities. Most notably, soil amendment with house cricket exuviae increased the relative abundances of the genera Lysinibacillus and Paenibacillus, whereas the other amendments did not. The exuviae of black soldier fly larvae, however, stimulated the genus Pseudomonas and different genera belonging to the Burkholderiaceae for a longer period of time than the exuviae of either other insect species. In view of the differential enrichment of potentially plant growth-promoting or plant-protective bacteria, soil amendments with the exuviae of different insect species might have specific uses in agriculture. The present study provides a basis for investigating the combined application of insect exuviae with beneficial bacteria that are commonly used in crop production.