Size matters: Micronutrient supplementation impacts development of Hermetia illucens (Diptera: Stratiomyidae) and Cochliomyia macellaria (Diptera: Calliphoridae)

Formulating diets for mass-produced insects is a key aspect of such systems. Failure to do so can result in mortality, poor growth, and low survivorship or reproduction. Historically, for the insects as food and feed industry, efforts have primarily focused on macronutrients, such as protein or carbohydrates. However, essential micronutrients, such as amino acids, minerals, and vitamins, also have similar impacts. A slight variation outside the required amount of a single micronutrient could be the difference between survival and death. A diet imbalanced in micronutrients could interrupt associated metabolic pathways and interactions vital for insect development. Tryptophan, an essential amino acid, has been shown to increase protein content, survivorship, and the body weight of insects when given supplemental dietary concentrations. Select metabolites of tryptophan impact zinc storage, demonstrating how one micronutrient can directly impact another. Larvae of Hermetia illucens (L.) (Diptera: Stratiomyidae) and Cochliomyia macellaria (F.) (Diptera: Calliphoridae), which can be mass-produced and used as feed, were placed in 50 mL Falcon tubes in groups of 20 on their respective control diets with a doubled concentration of tryptophan, zinc, or a combination. Replicates were held at 27°C and 65% relative humidity until the first 50% of the larval feeding stage was reached. Larval survivorship, weight, and feed conversion ratio were collected. Larval length and width were calculated using ImageJ software. Results demonstrated that supplementation of micronutrients did impact the life-history traits of both species, which can have implications within the mass-reared insect industry for diet optimization.