Fitness effects of synthetic and natural diet preservatives on the model insect, silkworm Bombyx mori

Silkworm (Bombyx mori) pupae are recognized as a novel, nutritionally valuable food source. It has the potential to serve as an alternative protein source for both human and animal nutrition. Silkworm rearing with artificial diet can be achieved throughout the year to ensure a sufficient supply of silkworm pupae. However, artificial diets are prone to spoilage caused by bacterial contamination. Here, we evaluated the efficacy of two different potential preservatives, ethylparaben (EP, a chemical synthetic substance) and medium-chain fatty acids (MCFAs, from natural sources), in the silkworm artificial diet, and examined their consequential dietary effects on the test organism. Our investigation revealed that both preservatives effectively inhibited pathogenic bacterial growth. Interestingly, the EP-supplemented diet increased body weight and silk production, while the MCFAs-supplemented and the control groups were on par. Furthermore, the addition of EP or MCFAs did not exert a negative impact on the homeostasis of gut microbiota. However, it is imperative to acknowledge that EP ingestion exhibits a certain degree of toxicity, as indicated by the silkworm transcriptome data, revealing the upregulation of detoxification-related genes such as Ugt2 and immune-related genes Cecropin B. Silkworm pupae being rich in protein, lipids, minerals, and vitamins are considered a good source of nutrients for humans. We need to consider the safety of silkworm pupae more thoroughly when using them. Therefore, as a natural preservative, MCFAs emerge as a suitable option from a safety perspective. These findings offer valuable direction for future research into the metabolic adaptation mechanism of mass-reared insects to diet preservatives, as well as to enhance silkworm artificial feeding formulas.