| The silkworm(Bombyx mori)is one of the important economic insects in China,with a history of more than 5,000 years of breeding,and has achieved great economic benefits.Silkworms reared with artificial diets during all instars have the advantages of standardizable,simplicity and efficiency,breaking seasonal and regional restrictions,reducing the risk of poisoning,and so on,is the future development direction of sericulture.However,compared with the traditional mulberry leaves breeding,there are still problems such as low silk yield and low cocoon shell rate,so failure to accomplish industrial farming of silkworms reared on artificial diets during all instars in production.In order to seek a breakthrough,we studied the spinning behavior,nutrient absorption,and transcriptomics of the silkworm.The results are as follows:(1)Effect of reared with artificial diets during all instars on the spinning and cocooning of the silkwormThe results of cocoon quality survey showed that there was no significant difference in cocooning rate(99.60%),dead silkworm cocoons rate(1.07%),and deformed cocoons rate(7.66%)between the silkworm reared with artificial diets and mulberry leaves during all instars.And the cocoon weight(1.10 g),cocoon shell weight(0.17 g),and cocoon shell rate(15.70%)in the silkworms reared on artificial diets were significantly lower than that of those reared on mulberry leaves(P < 0.001).Interestingly,the rate of the double cocoons(5.78%)in the silkworms reared on artificial diets was significantly higher than that of those reared on mulberry leaves(P < 0.01).Subsequently,the spitting behavior study results showed that the spinning duration(73.78 h)and crawling distance(307.16 cm)were significantly lower in the silkworms reared on artificial diets than reared on mulberry leaves(P < 0.01).The results showed that although the silkworm reared with artificial diets during all instars could still spin and pupate,the silk production and cocoon quality of the silkworm decreased,and the ability to find suitable cocoon environment was poor,leading to a significant increase in the number of double cocoons.2.Effect of reared with artificial diets during all instars on the development of the silkwormIn this study,the development of the 5th instar silkworm was investigated.The results showed that the body weight and silk gland weight were significantly lower in the silkworms reared on artificial diets than reared on mulberry leaves(P <0.001),and at the later stage of the 5th instar,the silk gland weight of the silkworms reared on artificial diets tended to decline,while those of the silkworms reared on mulberry leaves tended to be stable.The results of the silk gland tissue somatic index(SGTSI)survey show that SGTSI of both groups showed an increasing trend during the 5th instar,but the SGTSI of the silkworm reared on artificial diets was lower than that of reared on mulberry leaves at 24 h after the fifth instar first feeding,and then showed a rapid growth trend,which was significantly higher than that of reared on mulberry leaves at 48-120 h(P < 0.01),but lower than that of reared on mulberry leaves at 144-168 h.The results of the study indicated that the normal development of the individual and silk gland of the silkworm was affected by being reared on artificial diets during all instars.(3)Effect of reared with artificial diets during all instars on the nutrient uptake of the silkwormThe results of the determination of crude protein content in the diet showed that the crude protein content of the artificial diets suitable for feeding the 5th instar silkworm(163.29 g/kg)was significantly higher than that of mulberry leaves(P <0.001).However,the results of subsequent dietary efficiency surveys showed that the ingesta(2.18 g),digesta(0.61 g),approximate digestibility(28.12%),efficiency conversion of ingesta to cocoon(50.21%),efficiency conversion of ingesta to shell(7.88%),and efficiency conversion of digesta to shell(28.03%)of the silkworm reared on artificial diets were significantly lower than those reared on mulberry leaves,and only the efficiency conversion of digesta to cocoon(178.53%)was significantly higher than that reared on mulberry leaves(P < 0.01).As a result,the crude protein intake of the silkworm reared on artificial diets was lower than that of reared on mulberry leaves.The results showed that the digestion and absorption of nutrients in the silkworm reared on artificial diets were weak,and the nutrients were mainly used for silkworm body development,which affected the growth and development of silkworm and cocoon production.(4)Effect of reared with artificial diets during all instars on the gene expression in the silk gland of the silkwormThe RNA-Seq results showed that there were 386 differentially expressed genes between the two groups,of which 242 were up-regulated and 144 were downregulated.GO enrichment analysis showed that differentially expressed genes were mainly enriched in biological processes such as organic acid metabolism,oxidation-reduction,and drug catabolism.KEGG enrichment analysis showed that differentially expressed genes were mainly enriched in genetic information processing,amino acid metabolism,nucleotide metabolism,and carbohydrate metabolism pathways.After further screening,the differentially expressed genes related to amino acid transport,immunity,mitosis,energy metabolism,actin and hormone were obtained.In conclusion,reared with artificial diet during all instars reduced the dietary efficiency of the fifth instar silkworm,the activity of the silkworm during the wandering period and the spinning duration of the silkworm during the cocooning period,affecting the nutrient absorption and silk gland gene expression of the silkworm,resulting in significantly lower silk yield than the silkworm reared on mulberry leaf.Our results provide a reference for the breeding and application of industrial-rearing silkworms with artificial diets. |
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