Black soldier fly as feed for aquatic insects

Laboratory experiments on predatory aquatic insects have various practical challenges, including high nutritional demands of fresh prey. Ideally, predatory insects are reared with live prey that are easy to cultivate in laboratory environment, low-cost, rich in nutrients, and easily accessible. Here, we assess whether the black soldier fly (BSF) Hermetia illucens L. larvae and adults are suitable feed for major aquatic insect groups with distinct trophic niches (Odonata, Coleoptera, Hemiptera, Megaloptera). We first determined the size overlap between BSF larvae and major aquatic insect groups using existing databases of body size. We then experimentally assessed whether BSF larvae: 1) are consumed by different groups of predators, 2) can survive prolonged periods underwater, and 3) are selected based on body size. We found that the body size of BSF larvae overlaps with most insect groups, with smaller larval instars showing the highest overlap. Our feeding experiment showed that all predatory insect groups consumed BSF larvae, and could survive under a strict BSF diet for at least a few weeks. Insect floaters (water striders) and divers (backswimmers and diving beetles) consumed BSF adults regularly. BSF larvae sunk underwater and repeatedly performed undulating movements, making them detectable to predators. BSF larvae can survive underwater for extended periods (1-6 days), with larger instars surviving longer. For sit-and-wait predators such as odonates (dragonflies and damselflies), larvae were more likely to consume smaller BSF larvae. Our observed behavioral and physiological characteristics of the BSF suggest that it is a promising feed for various aquatic insects.