In silico identification and assessment of insecticide target sites in the genome of the small hive beetle, Aethina tumida

Abstract

Background: The small hive beetle, Aethina tumida, is a rapidly emerging global pest of honey bee colonies. Small hive beetle infestation can be extremely destructive, which may cause honey bees to abscond and render colony infrastructure unusable. Due to the impacts small hive beetles have on honey bees, a wide variety of physical, cultural, and chemical control measures have been implemented to manage small hive beetle infestations. The use of insecticides to control small hive beetle populations is an emerging management tactic. Currently, very little genomic information exists on insecticide target sites in the small hive beetle. Therefore, the objective of this study is to utilize focused in silico comparative genomics approaches to identify and assess the potential insecticide sensitivity of the major insecticide target sites in the small hive beetle genome. Results: No previously described resistance mutations were identified in any orthologs of insecticide target sites. Alternative exon use and A-to-I RNA editing were absent in AtumSC1. The ryanodine receptor in small hive beetle (Atum_Ryr) was highly conserved and no previously described resistance mutations were identified. A total of 12 nAChR subunits were identified with similar alternative exon use in other insects. Alternative exon use and critical structural features of the GABA-gated chloride channel subunits (Atum_RDL, Atum_GRD, and Atum_LCCH3) were conserved. Five splice variants were found for the glutamate-gated chloride channel subunit. Exon 3c of Atum_ GluCl may be a beetle-specific alternative exon. The co-occurrence of exons 9a and 9b in the pH-sensitive chloride channel (Atum_pHCl) is a unique combination that introduces sites of post-translational modification. The repertoire and alternative exon use for histamine-gated chloride channels (Atum-HisCl), octopamine (Atum_OctR) and tyramine receptors (Atum_TAR) were conserved. Conclusions: The recently published small hive beetle genome likely serves as a reference for insecticidesusceptible versions of insecticide target sites. These comparative in silico studies are the first step in discovering targets that can be exploited for small hive beetle-specific control as well as tracking changes in the frequency of resistance alleles as part of a resistance monitoring program. Comparative toxicity alongside honey bees is required to verify these in silico predictions.

The cys‐loop ligand‐gated ion channel gene superfamilies of the cockroaches Blattella germanica and Periplaneta americana

“…Blattella germanica and P. americana possess eight and ten divergent nAChR subunits, respectively. This is notably larger than in other genomes such as those of Aedes aegypti , Anopheles gambiae , Apis mellifera , Acyrthosiphon pisum , Aethina tumida , Bombyx mori , D. melanogaster , T. castaneum and N. vitripennis , which possess between one and seven divergent subunit genes 30,37–39,47–51 . Of the divergent nAChR subunits present in B. germanica , two are of the α subtype and six are β whereas there are one α and nine β in the P. americana genome (Figs 3 and 4).…”

“…In the genomes of B. germanica and P. americana , 17 and 19 candidate nAChR‐subunit encoding genes were identified, respectively (Figs 1, 3 and 4). This is larger than other insect nAChR gene families described, such as from D. melanogaster (ten subunits), 47 Anopheles gambiae (ten subunits), 48 Apis mellifera (11 subunits), 49 Aethina tumida (12), 39 Acyrthosiphon pisum (11 subunits), 50 Bombyx mori (12 subunits), 51 T. castaneum (12 subunits), 30 Aedes aegypti (14 subunits) 38 and N. vitripennis (16 subunits) 37 . Both B. germanica and P. americana possess typical core groups of nAChR subunits that are highly conserved in different insect species, 2 these being α1–α8 and β1 (Fig.…”

“…Using tBLASTn, 30 and 32 cysLGIC subunit genes were identified in the genomes of B. germanica and P. americana , respectively. These are notably large insect cysLGIC superfamilies considering that the previously identified superfamilies from genomes of Drosophila melanogaster , 35 Apis mellifera , 36 Tribolium castaneum , 30 Nasonia vitripennis , 37 Acyrthosiphon pisum , 29 Aedes aegypti 38 and Aethina tumida 39 consist of 21 to 26 genes 1 . An alignment of P. americana protein sequences shows that the cockroach subunits possess features characteristic to members of the cysLGIC superfamily 40 (Figs 1 and 2).…”

Cell lines derived from the small hive beetle, Aethina tumida, express insecticide targets

“…Total RNA was purified from each cell pellet using Trizol (ThermoFisher, Waltham, MA) reagent following the manufacturer's protocol. Purified RNA was (Evans et al 2018) and used to identify the SHB orthologues of genes that are commonly targeted by insecticides (Rinkevich and Bourgeois 2020). We evaluated the transcription of these insecticide targets in the three SHB sublines via tBLASTn analyses of the SHB cell line transcriptomes using Geneious software (Biomatters, Auckland, New Zealand).…”

“…We evaluated the transcription of these insecticide targets in the three SHB sublines via tBLASTn analyses of the SHB cell line transcriptomes using Geneious software (Biomatters, Auckland, New Zealand). Of the 47 candidate insecticide targets identified by Rinkevich and Bourgeois (2020), only five were expressed (FPKM >1) in any of the three SHB sublines. Transcripts were detected for three different acetylcholine receptor subunits, α1, α5 and α9, in the sublines derived from SHB eggs and neonates (AtumEN1129-D6 and -D12) but not in the subline derived from eggs alone (AtumE1127-B7).…”