The effect of Rhodococcus rhodochrous supplementation on black soldier fly (Diptera: Stratiomyidae) development, nutrition, and waste conversion

Abstract

Black soldier fly larvae are mass produced globally for use as livestock, poultry, and aquaculture feed. Efforts are continuously seeking processes optimising larval rate of growth, size, and waste conversion as a means to lower cost and increase output. Manipulating microbes in the larval substrate (i.e. fermentation or supplementation) has been demonstrated as a potential solution. However, identifying appropriate microbes for use in this process has been limited. The objective of this study was to determine whether supplementing black soldier fly larvae with the oleaginous microbe Rhodococcus rhodochrous would result in accelerated larval development, increased final larval body size, and increased conversion efficiency. Larvae fed a sterile, or non-sterile, diet treated with R. rhodochrous grew 3× faster than the control by the third day and were approximately 2× larger than the control by the conclusion of the experiment. Conversion rate was 2× greater for the treatments indicating less feed would be needed to achieve maximum weight gain. Protein composition of resulting larvae fed diet supplemented with R. rhodochrous, was significantly different than the control not receiving the microbial infusion. Larvae provided the microbe had 4.20 and 2.79% greater fatty acid composition and short-chained fatty acids, respectively, but lower monounsaturated fatty acids (1.60%) and polyunsaturated fatty acids (2.4%). Furthermore, larvae provided R. rhodochrous produced significantly more proteins related to energy production and storage, as well as muscle development and contraction, while those sans microbe, produced proteins related to stress responses (e.g. heat shock proteins). While, this study yielded positive results for the inclusion of R. rhodochrous as part of the black soldier fly larval diet, additional research is needed to optimise the dose at an industrial scale.