Why Researchers are Re-Creating an Infamous Hitchhiker’s Month-Long Journey Around the Globe
By Rob Morrison, Ph.D.
Recently, researchers at Lincoln University (in Christchurch) and Better Border Biosecurity in New Zealand teamed with scientists at the U.S. Department of Agriculture–Agricultural Research Service (USDA-ARS) to study the dynamics of diapausing invasive brown marmorated stink bug (Halyomorpha halys). Specifically, they sought to examine how the crop pest travels as a “stowaway” aboard cargo ships.
This journey from North America usually takes about a month to complete, going from the Northern Hemisphere to the Southern Hemisphere. The bugs can end up overwintering in goods being transported, for example inside shipping containers departing the Northern Hemisphere in the late autumn. A concern is that the bugs can become active by the time they reach New Zealand during summer in the Southern Hemisphere. In recent years, a number of ships from different parts of the world have been turned away from docking in New Zealand because stink bugs were found.
In particular, the research team, led by Laura Nixon, Ph.D., then a doctoral student at Lincoln University’s Bio-Protection Research Centre, set out to investigate better ways of detecting these hitchhiking brown marmorated stink bugs. Toward that end, they designed a study to simulate the pest’s voyages on the ocean. The results of their study were published in February in the Journal of Pest Science.
As ships cross from port to port, they undergo a circular, up-and-down movement caused by the waves, which stink bugs would experience in cargo containers. It was unknown whether this would disturb diapausing adults, prompting them to produce their characteristic “stink” or increase their mobility. Scientists at the USDA-ARS Appalachian Fruit Research Station in Kearneysville, West Virginia, mimicked this motion in the lab using a robotic arm (see picture and video). Diapausing stink bugs were loaded into a simulated cargo container, then attached to the end of the robotic arm. Using equations to describe the motion of waves, the robotic arm moved in parabolic circles for seven days. Afterward, the scientists simulated off-loading of cargo, which the robotic arm did by free-falling for three feet before coming to a sudden stop.
Periodically during this process, scientists sampled the air surrounding the stink bugs and examined it for key “stink” volatiles that would indicate the presence of the stink bugs. They also evaluated the bugs for their mobility. The eventual goal is to identify certain key compounds that port inspectors armed with electronic sniffing devices can use to evaluate whether stink bugs are present on ships—even when the pests can’t be easily detected visually because of their inactivity.
Based on their studies, the researchers found stink bugs under simulated ship movement did not release different compounds than stationary stink bugs, nor were there changes in mobility. The team detected releases of tridecane regardless of whether there was movement or not, suggesting it is a passive marker of brown marmorated stink bug. The team suspects that, over the course of the month-long journey, tridecane may accumulate in containers to detectable levels for port inspectors; however, future studies will need to confirm this.
In addition, the researchers evaluated diapausing stink bug mobility over a month-long period in environmental chambers that were programmed to gradually increase in temperature that would mimic the journey from fall to summer. While stink bugs were initially immobile, they became very active as the temperature increased across the gradient to the Southern Hemisphere, peaking at 15 days into the journey. By the end of the experiment period, the team observed high bug mortality and much lower mobility, likely because no food or moisture were present for the pests.
Taken together, these results provide new insights into the dynamics of diapausing aggregations during transport around the globe. The information in the study is useful for further risk assessment and greater understanding of potential invasion pathways to New Zealand, which should help inform biosecurity procedures going forward.
Journal of Pest Science
Rob Morrison, Ph.D., is a Research Entomologist at the USDA-Agricultural Research Service, Center for Grain and Animal Health Research, in the Stored Product Insects and Engineering Research Unit, in Manhattan, Kansas. Web: www.ars.usda.gov/pa/cgahr/spieru/morrison. Twitter: @morrisonlabUSDA. Email: firstname.lastname@example.org