Annotated draft genomes of two caddisfly species Plectrocnemia conspersa CURTIS and Hydropsyche tenuis NAVAS (Insecta: Trichoptera)

Members of the speciose insect order Trichoptera (caddisflies) provide important ecosystem services, e.g. nutrient cycling through breaking down of organic matter. They are also of industrial interest due to their larval silk secretions. These form the basis for their diverse case-making behavior that allows them to exploit a wide range of ecological niches. Only five genomes of this order have been published thus far, with variable qualities regarding continuity and completeness.

A low-cost sequencing strategy, i.e. using a single Oxford Nanopore flow cell per individual along with Illumina sequence reads was successfully used to generate high-quality genomes of two Trichoptera species, Plectrocnemia conspersa and Hydropsyche tenuis.

Of the de novo assembly methods compared, assembly of low coverage Nanopore reads (∼18-20x) and subsequent polishing with long reads followed by Illumina short reads (>100x coverage) yielded the highest genome quality both in terms of contiguity and BUSCO completeness. The presented genomes are the shortest to date and extend our knowledge of genome size across caddisfly families. The genomic region that encodes for light (L)-chain fibroin, a protein component of larval caddisfly silk was identified and compared with existing L-fibroin gene clusters.

The new genomic resources presented in this paper, are among the highest quality Trichoptera genomes and will increase the knowledge of this important insect order by serving as the basis for phylogenomic and comparative genomic studies.