Using insects for sustainable waste management of superabundant animals

The management of fecal waste from superabundant species in urban green spaces is a central topic in environmental sustainability and public health. In North America, the Canada goose (<i>Branta canadensis</i>) is particularly problematic because of its large abundance in public spaces, resulting in large quantities of droppings that negatively affect the recreational, aesthetic and hygienic quality of the environment. Here, we evaluate the potential of black soldier fly (BSF; <i>Hermetia illucens</i>) larvae to bioconvert Canada goose feces into protein, while producing frass that can be used as plant fertilizer. We performed an experiment that evaluates BSF performance (Larval growth performance, adult body weight, and adult lifespan) under three diet treatments: a standard Gainesville diet (F0-control), a mixed diet containing 50% goose feces and 50% Gainesville (F50), and a diet consisting entirely of goose feces (F100). Additionally, based on the key role that microbial communities play during BSF development and bioconversion, the treatments were also replicated using autoclaved-sterile diets to assess the effect of absence of fecal microbes. We also conducted an experiment that assessed growth performance of duckweed (<i>Lemna minor</i>) across different fertilization treatments, including Hoagland’s media (control), and three concentrations (2.5, 5, and 10 g·L^-1) of fresh goose feces and insect frass (derived from 100% goose feces). We found that the BSF larvae can survive and complete its larval development in both 50% and 100% fecal treatment diets, albeit the growth rate, adult body weight, and adult lifespan decreased with increasing concentration of feces. Sterilizing the feces had a positive effect on growth rates in F50 but a negative effect in F100. However, sterilization did not have a significant effect neither in the body weight nor in the lifespan of adults. Duckweed growth was the fastest in the frass treatment at concentrations of 10 g·L^-1, suggesting that BSF larvae increased the nutritional value of goose feces for duckweed. Our study suggests that BSF can be used to bioconvert Canada goose feces into protein while generating a valuable plant fertilizer.