Transcriptomic resources for Bagrada hilaris (Burmeister), a widespread invasive pest of Brassicales

Abstract

The bagrada bug, Bagrada hilaris (Burmeister), is an emerging agricultural pest in the Americas, threatening agricultural production in the southwestern United States, Mexico and Chile, as well as in the Old World (including Africa, South Asia and, more recently, Mediterranean areas of Europe). Substantive transcriptomic sequence resources for this damaging species would be beneficial towards understanding its capacity for developing insecticide resistance, identifying viruses that may be present throughout its population and identifying genes differentially expressed across life stages that could be exploited for biomolecular pesticide formulations. This study establishes B. hilaris transcriptomic resources for eggs, 2nd and 4th larval instars, as well as male and female adults. Three gene families involved in xenobiotic detoxification-glutathione S-transferases, carboxylesterases and cytochrome P450 monooxygenases-were phylogenetically characterized. These data were also qualitatively compared with previously published results for two closely related pentatomid species-the brown marmorated stink bug, Halyomorpha halys (Stål), and the harlequin bug, Murgantia histrionica (Hahn)-to elucidate shared enzymatic components of terpene-based sex pheromone biosynthetic pathways. Lastly, the sequence data were screened for potential RNAi- and virus-related content and for genes implicated in insect growth and development.

Fig 1. Glutathione S-transferase (GST) enzymes from B. hilaris.

Cladogram of bagrada bug GSTs distilled from the comprehensive, ten-taxa phylogram presented in S1 Fig. GST classes are connoted by leaf coloring: turquoise ~ Theta, green ~ microsomal, brown ~ Sigma, purple ~ prostaglandin E synthase, red ~ Delta, and black ~ not classified. (No Omega- or Epsilon-class sequences were observed in bagrada bug).

Fig 2. Carboxylesterase (COE) enzymes from B. hilaris.

Cladogram of bagrada bug COEs distilled from the comprehensive, ten-taxa phylogram presented in S3 Fig. COE classes are connoted using leaf coloring as follows: royal blue ~ β-esterases, purple ~ neuroligins, brown ~ acetylcholinesterases, turquoise ~ neurotactins, and gray ~ palmitoleoyl COE NOTUM.

Fig 3. Cytochrome P450 monooxygenase (CYP) enzymes from B. hilaris.

Cladogram of bagrada bug CYPs distilled from the comprehensive, ten-taxa phylogram presented in S5 Fig. CYP clans are indicated using leaf coloring: lime green ~ CYP2, orange ~ CYP3, turquoise ~ CYP4, and pink ~ Mito.

Fig 4. Hemipteran farnesyl diphosphate synthase (FDPS) and FDPS-like TPS (terpene synthase) phylogeny.

Leaf node identifiers are prefixed by species of origin: BBUG ~ Bagrada hilaris (bagrada bug), BMSB ~ Halyomorpha halys (brown marmorated stink bug), HBUG ~ Murgantia histrionica (harlequin bug), and SGSB ~ Nezara viridula (southern green stink bug). FDPS and TPS subfamilies are shown with leaf color coding: blue ~ canonical FDPS, yellow ~ TPS-a type clade (sesquipiperitol synthase-like), and green ~ TPS-b type clade. Leaf accessions correspond to NCBI protein database accession numbers for characterized hemipteran proteins or B. hilaris transcripts encoding the protein sequences. The phylogram was rooted to the canonical FDPS clade. Branch lengths are based on a JTT model of protein evolution and the scale bar denotes estimated amino acid substitutions per site. Node support from 3,000 bootstrap replicates is displayed in italic font.