Abstract
Halyomorpha halys is a major herbivore insect in the fruit orchards of China that has become a devastating invasive pest in North America and Europe since its accidental introductions in the 1990s and 2000s, respectively. Like other hemipteran insects, H. halys releases defensive chemicals against natural enemies, including (E)-2-decenal, which is an aldehyde associated with alarm pheromones. In this study, a series of electrophysiological and behavioral tests were conducted to characterize the alarm functions of (E)-2-decenal among H. halys adults and nymphs. An antennal transcriptome was obtained from a Chinese H. halys population, and 44 odorant-binding protein (OBP) genes were annotated. Among them, five putative alarm pheromone-binding proteins were screened and were extremely consistent with their homologs from US populations. These five OBPs were later expressed in a heterologous expression system, harvested, and then challenged with (E)-2-decenal in a binding assay. All five OBPs showed high binding activities to (E)-2-decenal, which demonstrated its behavioral significance as a defensive component in H. halys, as well as being the first report of its olfactory reception. These findings will help develop behavioral-mediating tools as part of integrated pest management approaches to control this invasive pest.
Highlights
Stink bugs (Hemiptera: Pentatomidae) employ a spectrum of volatile compounds that have ecologically significant roles in colonization, courtship, immunity, and chemical defense (Noge et al, 2015; Weber et al, 2017b)
We investigated the alarm effects of (E)-2-decenal and its olfactory preferences in H. halys by conducting electroantennogram (EAG) tests, behavioral assays with grouped or individual H. halys, antennal transcriptome analyses, and binding activity assays with putative odorant-binding protein (OBP)
By aligning the amino acid sequences of H. halys OBPs, we found that 36 out of 44 OBPs contained the normal six conserved Cys residues, indicating that the predicted C-pattern motif was indicative of a classic OBP in insects (Xu et al, 2009)
Summary
Stink bugs (Hemiptera: Pentatomidae) employ a spectrum of volatile compounds that have ecologically significant roles in colonization, courtship, immunity, and chemical defense (Noge et al, 2015; Weber et al, 2017b) Among these compounds, alarm pheromones, which mostly consist of short-chain aliphatic aldehydes, alcohols and esters, alkanes, terpenes, and phenolics, are well-known signature odorant cues in stink bugs (Aldrich, 1988; Millar, 2005; Moraes et al, 2008; Noge and Becerra, 2012). This work provides strong behavioral evidence and molecular olfactory bases to demonstrate the function of (E)-2-decenal as an alarm pheromone component in H. halys
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