Effects of amending soil with black soldier fly frass on survival and growth of the cabbage root fly (Delia radicum) depend on soil type

Abstract

New approaches to managing the cabbage root fly (Delia radicum L.) are needed because pesticide regulations continue to limit the availability of effective control products. Soil amendment with black soldier fly (Hermetia illucens L.) frass has recently been shown to reduce D. radicum survival. In a greenhouse experiment, soil from a field on which brassicaceous plant species had repeatedly been grown (brassica field soil) was mixed with frass at ratios of 1, 2 or 5 g/kg. In a second greenhouse experiment, 5 g/kg were added to (a) brassica field soil, (b) soil from a different field on which non-brassicaceous species had been rotated (crop rotation field soil) or (c) blocks of potting soil that were later transplanted to unamended field soil. Brussels sprouts (Brassica oleracea L.) plants were grown in amended soil and were infested with D. radicum larvae after 4 weeks. While amendment with 1 or 2 g/kg did not affect D. radicum performance compared with unamended soil, 5 g/kg reduced D. radicum survival and pupal biomass in brassica field soil. In crop rotation field soil, amendment with 5 g/kg reduced pupal biomass but did not reduce D. radicum survival. Amendment with 5 g/kg had no effect on D. radicum performance in potting soil. In general, D. radicum survival was lower in brassica field soil than in either other soil, irrespective of soil amendment. The effects of black soldier fly frass on D. radicum appear to depend on soil type.

Effects of frass from larvae of black soldier fly (Hermetia illucens) and yellow mealworm (Tenebrio molitor) on growth and insect resistance in field mustard (Brassica rapa): differences between insect species and frass treatments

“…These findings suggest that the frass application negatively affected D. radicum larvae in the soil and P. xylostella larvae feeding on the leaves of B. rapa. However, it is important to note that the effectiveness of BSFF to control pests may vary depending on the specific properties of both the frass and the soil type used (Wantulla et al, 2024). Although the activation of plant defensive responses following frass treatments has been attributed to the presence of eliciting molecules or microorganisms (Poveda, 2021), the particular mechanisms responsible for the lower herbivore performance in soil amendments with raw BSFF in the current study remain to be elucidated to assess their potential to contribute to pest management in agriculture.…”