Black soldier fly larvae show a stronger preference for manure than for a mass-rearing diet

The attention for black soldier fly larvae (BSFL) as an alternative ingredient for food and feed products is on the rise. While many studies have reported the efficiency of BSFL to bio-convert a wide range of organic waste streams into larval biomass, so far, it is unknown whether BSFL prefer certain waste streams over others when they have the possibility to choose. Here, we performed a choice-test experiment to explore the preference of BSFL when exposed to pig manure and a mass-rearing diet consisting of plant by-products currently used for industrial BSFL production. We found that after 1 hr of exposure to both feeds, BSFL strongly preferred pig manure over the mass-rearing diet. The preference for manure became stronger as larval age increased. Our results provide the first evidence that BSFL express a distinct diet preference. Understanding the reasons for the strong preference for manure is relevant for a diverse array of practical applications and to inform the discussion on insect welfare.