A novel approach to assessing human assisted insect dispersal on vehicles

Humans are transporting insects to novel locations at an increasing rate. This accidental movement can have dire consequences when invasive species successfully establish in new areas. Unfortunately, these patterns of movement have historically only been noted in retrospect. The spotted lanternfly (SLF, Lycorma delicatula (White)), a significant pest of winegrape and other crops, was brought to the United States from its native range on a cargo shipment of landscaping stone in 2014. Since first establishing in Pennsylvania, new breeding populations of SLF have been found in metropolitan areas in other states far removed from any known, existing population. This long-distance dispersal is likely the result of human-mediated hitchhiking on various modes of transportation including vehicles, cargo trucks, and freight trains. This movement may be exacerbated by the presence of tree of heaven (Ailanthus altissima (Mill.) Swingle), a significant host plant of SLF commonly found growing in disturbed areas bordering transportation corridors. However, how long a particular invasive insect species can be retained on a moving vehicle or train is either unknown or based on anecdotal observations.
We address this significant gap in invasive species research by designing the first system to test an insect’s capability to travel on the exterior of a passenger vehicle. We developed a laminar flow wind machine to test SLF adhesion to a vehicle's surface at wind speeds up to approximately 85 kilometers per hour. All four nymphal stages were evaluated along with two adult time periods, one representing the early season where SLF are rather small and reproductively immature, and later season when females especially are much larger in size and actively egg laying. This study offers the first empirical test to corroborate prior anecdotal reporting of SLF dispersal by vehicular movement. Our next steps include incorporating these data into a model to look at potential rates of spread from infested areas. We expect this system can easily be applied to other invasive species or adapted to test other modes of transportation.