Experimental evidence supports the ability of spotted lanternfly to hitchhike on vehicle exteriors as a mechanism for anthropogenic dispersal

Abstract

Historically, anecdotal observations support the likelihood of human-assisted invasive insect dispersal to new environments. No previous studies have investigated the ability of insects to remain attached to moving vehicles; however, such information is critical for prioritizing research, mitigation activities and understanding anthropogenic effects on biotic communities. Lycorma delicatula (White), spotted lanternfly (SLF), an invasive insect whose range is currently expanding throughout the United States, is commonly observed in urban settings and near transportation hubs. We developed a novel method to test SLF's ability to remain on vehicle surfaces including bonnet, nose wing, windscreen, wipers and scuttle panel using laminar wind flow from 0 to 100 ± 5 km h^-1. We found all mobile life stages (nymphs and adults) could remain on the vehicle up to 100 km h^-1. First instar nymphs and early season adults remained attached at significantly higher wind speeds than other stages. A brief acclimatization period prior to wind delivery increased attachment duration for all life stages except later season adults. The importance of outliers in the success of invasive species is well established. Given these results, any hitchhiking SLF could potentially establish incipient populations. This methodology will be beneficial for exploring human-assisted dispersal of other invasive arthropods.

Keywords: Lycorma delicatula; human-assisted spread; non-random spread; population dispersal; range expansion; spotted lanternfly.

Figure 1.

Experimental set-up of the laminar flow fan and vehicle placement. (a) Fan in horizontal position, situated just above and in line with the end of the bonnet. The anemometer was placed to the right of the tape mark, the insect starting position on the left. (b) The fan was rotated 90° into a vertical position when testing the offside nose wing. Insects began the assay just above the tape mark. (c) The fan was attached to a steel base; the power mover and the rest of the hydraulic system were located behind.

Figure 2.

Successful adhesion by acclimatized insects until maximum wind speed was reached. For each vehicle location, the value within each circle represents the percentage of total insects that reached the maximum wind speed without detaching (n = 180 ± 2 insects per location except at nose wing (n = 151), due to the high number of non-responders, table 1). The colour and relative size of the circle segments represent the proportion of that percentage contributed by that life stage (see table 1 for numerical representation). The colour associated with each insect stage is defined by the background colour of the lower left panel. Only stages where at least one individual reached the maximum speed are displayed in the circle. Location on vehicle: F_4,868 = 63.38, p < 0.001. Vehicle locations followed by the same letter are statistically equivalent at α = 0.05, Tukey test.

Figure 3.

Mean detachment wind speeds at each vehicle location by insect stage. (a) Bonnet, (b) nose wing, (c) windscreen, (d) scuttle panel and (e) wiper blade. Location on vehicle: F_4,868 = 46.24, p < 0.001. Letters following the vehicle location and under each life stage shows pairwise mean differences either between locations (lowercase) or among life stages within a given location (uppercase). Vehicle locations and life stages sharing the same letter and case are not statistically different at α = 0.05.

Figure 4.

Effect of sex on insect attachment. Average wind speed at detachment of male and female SLF across all testing locations; F_1,139 = 14.7, p < 0.001.

Figure 5.

Effect of body size on adhesion ability of late season adult SLF. The number appearing below each bar represent the number of individuals (n) tested per category. Light grey bars represent female SLF, dark grey bars represent male SLF. F_3,41 = 6.95, p < 0.001.

Figure 6.

Effects of acclimatization versus no acclimatization. Acclimatization: F_1,348 = 11.49, p < 0.001; life stage: F_5,348 = 29.41, p < 0.001; acclimatization × life stage: F_5,348 = 18.31, p < 0.001. Letters shared among insect life stages are not different statistically (Tukey test, α = 0.05).