Purpose: This study aimed to assess the microbiological and chemical risks from rearing black soldier fly larvae on solid pig manure. Additionally, two washing procedures were evaluated.
Methods: Larvae of the black soldier fly were reared at 24°C for 20 days until fully grown, with fresh pig manure as substrate. This manure was spiked with Listeria spp. or sulfadiazine, lincomycin, and doxycycline. Fresh manure, harvested larvae, and residual substrate were analysed for dry matter content and microbiology. Larvae were washed with a physiological water (10 washing steps) and with ethanol; both were analysed. Fresh manure and harvested larvae from the chemical hazard trial were, also, analysed for the presence of antibiotics.
Results: A microbiological hazard of rearing insects on the solid fraction of fresh pig manure seems to be present for certain bacterial groups. Escherichia coli and Listeria spp. disappeared after insect farming: they were no longer present in the residual substrate or the larvae. Yeast and fungi slightly decreased in the residual substrate. Salmonella, as well as sulfite-reducing anaerobic organisms decreased in both larvae and residual substrate. Washing the larvae did not decrease the number of microorganisms found. For the spiked antibiotics, carry-over percentages from the manure to the larvae was between 0.12% and 0.83%.
Significance: A transfer of microorganisms and antibiotics from the substrate to the larval biomass was found. For the growing stage, we could not establish an effective washing procedure. Farming insects for feed or food certainly needs special attention.