De Novo characterization of transcriptomes from two North American Papaipema stem-borers (Lepidoptera: Noctuidae)

Stem-borers in the genus Papaipema (Lepidoptera: Noctuidae) range from highly polyphagous agricultural pests to specialists on more than 20 families of flowering plants, many of them highly toxic. Papaipema is the largest genus of noctuids endemic to North America and provides an excellent study system for the evolution of noctuid host plant use. To improve the availability of genomic resources for such investigations, we performed de novo transcriptome sequencing and assembly for two specialist Papaipema with unusual larval hosts: P. speciosissima, which is associated with ferns, and the undescribed P. "sp. 4," which is associated with bamboo. The resulting transcriptomes were similar in terms of completeness, gene count, and gene identity, but we identified some 8,000 genes (~17% of each transcriptome) not shared between the two species. While some of these have identifiable orthologs in other Lepidoptera, ~5% of each transcriptome consists of species-specific genes. We examine the function of these genes and find that almost half have retrotransposon-related functional domains. The potential role of species-specific genes is discussed, and the expansion of certain retrotransposon families in Papaipema is examined.