Boosting Bug Farms: A Meta-Analysis on Probiotic Effects in Insect Rearing

Interest in insects and food as feed is rapidly growing. With this, however, comes a move towards mass rearing and industrial scale production. This upscaling and industrialisation of the rearing process is likely to result in high density rearing, which in itself facilitates disease spread (Tarwater and Martin, 2001). Furthermore, the fact that these insects are likely to be genetically closely related further increase the risk of infectious disease outbreak (Ekroth et al., 2019; Gibson and Nguyen, 2021). In tackling this risk, it is important that we do not resort to the mass use of antibiotics that has been seen in the livestock industry. Instead, alternative rearing practices should be developed. A practice that has received a huge increase in attention in the last years is the idea that supplementation of insect feed with probiotics could improve insect health and prevent pathogen spread. We carried out a meta-analysis to systematically analyse the data on probiotic supplementation of insects reared for food and feed available to date. The most commonly measured response to probiotic supplementation was body weight gain followed by microbiome diversity. For body weight gain, we collected 71 effect sizes from 28 studies and for microbiome diversity ten effect sizes from six studies. We found that overall, probiotics tended to increase insect growth rate but did not significantly impact microbiome diversity. Our analysis also highlighted two key literature gaps. To date, data are only available on one of the four insect species able to be sold as food in the EU, Tenebrio molitor. Furthermore, there are currently only very few studies that have looked at protection against pathogens by probiotic bacteria in insects reared for food and feed. So far, the data look promising, but data on more insect species and looking at inhibitory effects against pathogens are urgently needed.