High protein diets early in life improve survival, reduce cannibalism, and increase growth and yield in farmed yellow mealworms

In the wild, animals may be able to compensate for nutritional inadequacies through foraging for novel resources; however, on farms, animals have more limited nutritional options. Therefore, providing adequate and accessible nutrition is essential to positive farmed animal welfare. Billions of yellow mealworms (Tenebrio molitor; Coleoptera: Tenebrionidae) are farmed as mini-livestock each year for use as food and feed. The major feedstock used, wheat bran, can sustain complete development of the species, but has been shown to have significantly lower protein content than yellow mealworms would typically self-select, particularly at early developmental stages. This can reduce growth, survival, and adult oviposition, and may contribute to high rates of cannibalistic behaviour among larvae (as larvae may have few options but to seek protein from the bodies of conspecifics). In this study, we use 20% nutritional yeast as a dietary protein supplement for larvae in early (0-4 weeks) and later life (4-8 weeks) to assess the effects on survival, growth rate, and rates of cannibalism, as well as any effects on growth, development timing, and adult body size. We also investigated the impact of this higher protein diet, when fed to either larvae or adults, on fecundity. We find that protein supplementation in larval diets increased survival by 23%, growth rate by 200%, and total biomass at eight weeks by up to 272%. Larval cannibalistic behaviour was reduced and development time was shorter. The high protein diet, whether fed to adults or to larvae, increased the number of offspring per female by 34-36%. Survival and growth benefits of protein supplementation were especially pronounced when fed to early juvenile instars, but can benefit mealworms across the entire first eight weeks of development. We highlight the need for further research into dietary protein supplementation for yellow mealworms across development to better align with their dietary choices, thereby improving fitness, yield, and welfare.