Super silkworm cocoons constructed by multi-silkworm larvae: Promising composites with dense structures and excellent mechanical properties.

A normal silkworm cocoon (NSC) with a unique nonwoven structure is usually spun by a single silkworm larva. Notably, there is a special Bombyx mori genetic resource that many (three or more) mature larvae tend to collectively spin into one cocoon, which was named "multi-silkworm cocoon" ("MSC"). However, the MSCs display loose structure and poor mechanical properties which limits their further application. In this study, a series of hybrid silkworm cocoons (HMSCs) are obtained by hybridizing "MSC" with a selected commercial silkworm strain successfully. The morphology, microstructures, and mechanical properties of cocoons constructed by one to three silkworm larvae were characterized and compared. The results indicated that about 48.3 % of silkworm larvae could create double and triple cocoons in the F1 generation of the silkworm hybrid, displaying robust fiber networks and dense structures. The mechanical characteristics of the HMSCs, including the tensile, peeling, compression, and needle penetration resistance properties, exceeded those of MSCs, showing significant application potential for high-performance bio-composites. This study provides a practical approach for obtaining silkworm cocoons with controllable structures and mechanical properties to develop and fabricate natural composite and biomimetic materials.

High-resolution silkworm pan-genome provides genetic insights into artificial selection and ecological adaptation.

The silkworm Bombyx mori is an important economic insect for producing silk, the "queen of fabrics". The currently available genomes limit the understanding of its genetic diversity and the discovery of valuable alleles for breeding. Here, we deeply re-sequence 1,078 silkworms and assemble long-read genomes for 545 representatives. We construct a high-resolution pan-genome dataset representing almost the entire genomic content in the silkworm. We find that the silkworm population harbors a high density of genomic variants and identify 7308 new genes, 4260 (22%) core genes, and 3,432,266 non-redundant structure variations (SVs). We reveal hundreds of genes and SVs that may contribute to the artificial selection (domestication and breeding) of silkworm. Further, we focus on four genes responsible, respectively, for two economic (silk yield and silk fineness) and two ecologically adaptive traits (egg diapause and aposematic coloration). Taken together, our population-scale genomic resources will promote functional genomics studies and breeding improvement for silkworm.

Structure analysis of the spinneret from Bombyx mori and its influence on silk qualities.

Silk is an excellent natural fiber, which has been widely used in versatile fields. Silk spinning is a complex process involving the larval spinneret. The spinneret is essential for silk spinning, but the sectional morphology of the spinneret that determines the silk monofilament, the muscular activities around the silk press as well as the relationships between the spinneret and the properties of the resulting silk remain poorly understood. We studied these factors by dissecting the spinneret and analyzing silk from different Bombyx mori strains. The sectional morphology of silk monofilament was found to be largely determined by the spinneret, especially by the silk press. Moreover, contractile activity of the muscles around the silk press is high, and the contraction frequency of the muscles was estimated to range from 11.42 to 50 HZ. A comparison of the fibroin filaments before they entered the common tube indicated that the spinneret determines both silk shape and silk size. This study provides insight into the silk spinning process, which may help develop bionic spinning in further studies and also provides a rationale to study the effect of the spinneret on silk fineness at the molecular level.