Evaluation of the decomposition ability and characteristics of pig manure treated with different larval instar stages of black soldier fly (Hermetia illucens L.)

Waste treatment using black soldier fly (BSF; Hermetia illucens L.) larvae is an emerging technology that reduces livestock manure disposal. This study aimed to evaluate the effect of different growth stage BSF larvae on the decomposition potential (Experiment 1) and characteristics (Experiment 2) of pig manure. BSF larval instars were randomly divided in three groups according to their developmental stage, with three replicates per group, using a randomized block design. Each treatment group consisted of 1 kg of 2nd, 3rd, or 4th instar BSF larvae added in 10 kg of pig manure (Group 1, 2, or 3, respectively). In Experiment 1, 2nd and 3rd instar BSF larvae treatments resulted in greater decomposition levels of pig manure compared with 4th instar BSF larvae groups. In Experiment 2, BSF larvae improved the nutrient content of manure, leading to an increase in the total nitrogen levels and a decrease in total carbon content and C:N ratio, rendering it suitable for use as an organic fertilizer. In addition, the increased N levels of treated BSF manure were not related to lower pH levels. BSF larvae can greatly reduce ADF and NDF pig manure contents as a result of the larvae's waste reduction potential. Overall, BSF 3rd instar larvae have proven to be a useful tool for the sustainable management of pig manure by strongly increasing its decomposition ability and can be an organic fertilizer for agricultural purposes that reduce ADF and NDF contents through composting.