# Comparative Study of the Productive Parameters of Two Breeds of the Bombyx mori Silkworm Fed Rhodotorula glutinis Yeast

## TL;DR

This study compares how adding Rhodotorula glutinis yeast to the diet of two silkworm breeds affects their growth and productivity, finding optimal benefits at a specific concentration.

## Contribution

The study introduces the use of Rhodotorula glutinis yeast in silkworm diets to enhance productivity and identifies an optimal concentration for growth.

## Key findings

- Line C silkworms showed improved productive traits when fed with Rhodotorula glutinis at 1 × 10⁷ CFU/mL.
- Higher concentrations of yeast led to a decline in growth parameters, suggesting an optimal dosage.
- Positive correlations were found between larval and silk gland weights and other productivity indicators.

## Abstract

As a promising approach to strengthening the health and performance of Bombyx mori silkworms, microorganisms have features that can enhance the nutritional value of conventionally used mulberry leaves by stimulating growth, productivity, and disease resistance. To this end, Rodotorula glutinis yeast has unquestionable advantages, such as the ability to generate a variety of industrially valuable metabolites, including proteins and lipids, while being important for health via fatty acids, carotenoids, and enzymes. Although studies on animals have established the effectiveness of these yeasts, research has also revealed that they can have negative effects on immunocompromised individuals, which has led to controversies regarding their use. Less known as a mode of action in insects, R. glutinis demonstrates the important ability to beneficially impact growth and economic performance. In this study, we show that adding R. glutinis yeast to the diet of silkworms strengthens the effect of mulberry leaves, which leads to superior results in the B. mori silkworm, particularly in Line C, although a decrease was observed after a certain point.

In this study, a comparative approach was used with the aim of filling the knowledge gap regarding the productive and economic parameters of two native B. mori silkworm breeds (Lines C and Z) fed with different diets, namely mulberry leaves alone and mulberry leaves with R. glutinis yeast at two different concentrations (1 × 109 and 1 × 107 CFU/mL). The trifactorial experiment was carried out with 600 silkworms during the fifth instar, with 300 for each breed and 50 larvae per rearing tray. The larvae were randomly assigned into three feeding groups, with two replicates: in the control group (C), the larvae received ordinary mulberry leaves; in the first experimental group (RG-1), the larvae were given mulberry leaves supplemented with R. glutinis yeast at a 1 × 107 concentration; and in the second experimental group (RG-2), the larvae received the same quantity of mulberry leaves as the C and RG-1 groups, but with R. glutinis yeast at a 1 × 109 concentration. Line C larvae in the RG-1 group revealed higher values for most of the productive traits assessed. There was a positive and significant correlation between the weights and lengths of the larvae and the silk gland, the silk gland and the shell, the cocoon and the pupae and the shell, and the shell and the pupa size (p < 0.001). The steady decline in the parameters at a higher concentration suggests that R. glutinis positively influences a number of silkworm growth features at a recommended dosage of 1 × 107; however, further research is required to more precisely identify the mechanisms involved.