Insect rearing on manure: Are microorganisms and antibiotics being transferred from the substrate to the larvae?

Insects are believed to be a sustainable protein alternative for feed and food, however, food safety is an important factor. The substrate used is known to be important in the biological and chemical hazards of the non-processed insects. This study assessed the microbiological and chemical risks from rearing black soldier fly larvae on solid pig manure and evaluated two washing procedures. Manure was spiked with Listeria spp. or sulfadiazine, lincomycine, 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 and analysed in both cases. Fresh manure and harvested larvae of the chemical hazard trial were also analysed for the presence of antibiotics.
A transfer of micro-organisms and antibiotics from the substrate to the larval biomass was found. In contrast, E. coli and Listeria spp. disappeared after insect farming. For the growing stage, we could not establish an effective washing procedure. For the spiked antibiotics, carry-over percentages from the manure to the larvae between 0.12% and 0.83% were found.