Influence of diet on initial mating behaviour in the black soldier fly (Hermetia illucens)

Abstract The black soldier fly (BSF; Hermetia illucens ) is widely used as a waste converter and novel protein source in feed. Its larvae can convert a wide range of organic feed substrates that vary in nutritional quality, into biomass. Our aim was to investigate whether larval and/or adult diet impact BSF body weight, pupal duration and reproductive behaviour. We focussed on comparing low- and high-nutrient larval diets as well as the presence or absence of food in the adult stage. Experimental cages were specifically designed to accommodate lekking behaviour. To promote BSF reproductive behaviour, UV, green and blue LED lights were provided, in addition to fluorescent strip lights. We quantified the time to first mating attempt and first mating, the number of mating attempts and mating events, mating success and the influence of wing fanning on mating success by analysing one-hour video recordings. Courtship duration, copulation duration and male–male interactions were quantified. Our results show that both male and female flies reared on a high-nutrient larval diet had a greater body weight and longer pupation time. Among BSF reared on the low-nutrient diet, longer duration of pupation was associated with increased adult body weight. Mating behaviour, especially copulation time, was influenced by both larval-diet nutrient content and the availability of food during the adult stage. Flies reared on a low-nutrient larval diet exhibited longer copulation duration than those on a high-nutrient diet. Availability of food in the adult stage had the most pronounced influence on mating behaviour: the absence of food resulted in earlier and more frequent mating attempts, a shorter wing-fanning duration and a longer copulation time. These results highlight the importance of diet for body weight, pupal duration and reproductive behaviour. Understanding these effects is relevant for optimising mass-rearing conditions and improving BSF welfare in commercial production systems.