The Anti-malnutrition Effect of Fulvic Acid from Yunnan Young Brown Coal in Silkworms

Abstract

Mulberry powdery mildew often leads to a severe loss in cocoon production during the late autumn silkworm season. We investigated if fulvic acid sodium (FANa) from Yunnan young brown coal could reduce such losses. We examined the effects of FANa on 9 types of bacteria isolated from diseased silkworms, and we examined its effects on starvation resistance and high-temperature survival of silkworms. The results indicated that FANa had no noticeable influence on bacteria, but it significantly increased survival of silkworms during fasting and in high-temperature conditions (increased 12.21 and 24.16%, respectively, p < 0.05). Finally, we evaluated if FANa could reduce malnutrition of silkworms caused by diseased mulberry leaf ingestion and tested it in a mulberry-reducing model. Compared to the control group, the model group (given 80% of leaves) significantly delayed the spinning time (3 days, p < 0.0001), decreased cocoon weight (28% less, p < 0.05) and reduced cocoon production (41% less, p < 0.0001). However, addition of 4% FANa shortened the larval stage (2 days, p < 0.01), and it saved 27% of leaves and 22% of work time. Moreover, FANa increased the cocoon weight (101% of control, p < 0.05) and increased cocoon production (79% of control, p < 0.05) compared to the model group. Taken together, these results suggest that FANa can improve resistance to malnutrition in silkworms and reduce the loss caused by mulberry powdery mildew.