Behavioural responses of diapausing Halyomorpha halys (Hemiptera: Pentatomidae) to conspecific volatile organic compounds.
The brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae), is an invasive pest in America, Europe and Asia and causes serious economic loss to crops, and nuisance problems during overwintering. Uninvaded southern hemisphere countries, such as New Zealand and Australia, see an increase in H. halys border interceptions during the northern hemisphere populations' overwintering period as large aggregations of H. halys can settle to diapause in items for export, e.g. vehicles, containers, etc. Here, we explored aspects of diapausing H. halys behaviour relative to release and perception of defensive odour compounds. First, to determine whether group size and agitation affect the release of defensive odours, diapausing H. halys were confined in glass tubes as individuals or in varying group sizes and mechanically agitated or remained stationary and the presence or absence of defensive odours was recorded. Using gas chromatography-mass spectrometry, we also established if exposure to individual defensive odour components (tridecane, (E)-2-decenal, 4-oxo-(E)-2-hexenal, and dodecane) induced individuals to release defensive compounds. Additionally, H. halys dispersal was measured in the laboratory following exposure to individual components of their defensive odour or their natural blend. We found that agitating individual bugs did not induce the release of defensive odours. The release of human-detectable odours was only found in groups of mechanically agitated H. halys, whereas non-agitated bugs did not emit odour. Exposure to 4-oxo-(E)-2-hexenal was the only odour component that resulted in individual H. halys releasing defensive compounds. Diapausing H. halys exposure to the natural blend of defensive compounds resulted in increased horizontal distance moved and velocity, while tridecane exposure increased distance moved, velocity and angular velocity, and (E)-2-decenal exposure increased distance moved. Our behavioural and chemical data suggest that defensive compounds released by diapausing H. halys act as an alarm pheromone, particularly when adults are in aggregations.