Feeding habits of spotted lanternflies in a forest of eastern Pennsylvania

Student research blog by Jon Krupnick, Earth & Environmental Science Major, Lehigh University.

Photo: Jon Krupnick

The spotted lanternfly (Lycorma delicatula) is an invasive species in the Fulgoridae family of insects. Native to eastern China, India, and Vietnam, it invaded eastern Pennsylvania in 2014 (Liu et al., 2017). Spotted lanternflies feed on sap from a range of plant species and pose a significant threat to agriculture and native ecological communities (Liu et al., 2017). Much research has focused on agricultural impacts; however, little is known about their potential effects on forested ecosystems. While spotted lanternflies are known to prefer the tree of heaven (Ailanthus altissima), a species from their native range, they have also been observed feeding on at least 70 other species (Kim et al., 2011; Dara et al., 2015). 

Observing spotted lanternflies.

To help anticipate potential impacts of this new invasive species, I collected baseline ecological data assessing the lanternfly’s feeding preferences in the forest of South Mountain near Bethlehem, Pennsylvania. Specifically, I assessed 1) whether different life stages of the spotted lanternfly feed on different species and 2) whether their feeding reflected the abundance and availability of plant species in the surrounding forest or real preference for particular plant species.

To do this, I conducted repeated surveys of ~75-acres of forest (Figure 1) from early July through the end of August 2020, recording the density of spotted lanternflies on trees, vines, and shrubs. Host plant species were marked and numbered with flagging tape, coordinates were recorded using Gaia GPS, and locations were plotted in Arcmap (Figure 2). Each day a subset of the affected plants were visited, and changes in the number of spotted lanternflies of different life stages were recorded. To assess whether spotted lanternflies were targeting particular plant species at greater rates than their abundance in the surrounding forest, I also identified the three nearest, non-affected plant species at each of the trees, shrubs, and vines used by the lanternflies.

Figure 1. Location of the 75 acres of forest on South Mountain near Lehigh University where this study was performed. The entire area was hiked weekly during summer of 2020, focusing on a different subsection each day.

Figure 2. Location of plant species used by spotted lanterflies on South Mountain in the summer of 2020.

Lanternflies were observed feeding on a total of 186 individual plants (Figure 2) representing 21 different plant species. Results indicate clear feeding preferences, with substantial differences across life stages (Figure 3). Earlier life stages fed on a broad range of species, but as the lanternfly progressed through its life stages it increasingly focused on tree of heaven, with a small portion of adults feeding on black walnut and grape (Figure 3).

Figure 3. Relative abundance of spotted lanternflies of different life stages using different plant species on South Mountain in summer 2020.

More detailed information on the shifting trends of feeding preference, and actual numbers of spotted lanternflies, can be found in Figure 4. Decreasing trends of spotted lanternfly use were observed during the late summer for grape, silverbell, bittersweet, and devil’s walking stick. The use of black walnut by spotted lanternflies peaked during mid August when the 4th instar nymphs were at their maximum abundance. The vast majority of adult lanternflies used tree of heaven. 

Figure 4. Actual numbers of spotted lanternflies feeding on native and invasive plant species on South Mountain over 8 weeks from July until late August.

Plant species targeted at higher rates than what would be expected given their availability in the forest included grape (Vitis sp.), tree of heaven, black walnut (Juglans nigra), devil’s walking stick (Aralia spinosa), and oriental bittersweet (Celastrus orbiculatus) (Figure 5). Some species, including grape and tree of heaven, were clearly used at higher rates than their abundance in the forest, suggesting real preferences for these food sources by the spotted lanternfly. Other trees like oak were found to host lanternflies but at much lower rates than their availability in the forest would suggest, suggesting that the insects tend to avoid these.

Recent research has demonstrated that spotted lanternflies sequester toxins from tree of heaven as a defense against predation (Song et al. 2018). Several targeted plant species on South Mountain, like black walnut, oriental bittersweet, and devil’s walking stick also contain toxic chemical compounds, and perhaps spotted lanternfly are using them in a similar way. Additional research is needed to better understand spotted lanternfly feeding preferences and to determine potential relationships with the chemical content of host plant species.

Figure 5. The plot on the left shoes an estimate of the relative abundance of potential plant species that could be used by spotted lanternflies in the study area, as indicated by identifying woody plants nearby those used by spotted lanternflies, in addition to those actually used by the insects. The plot to the right shows woody species targeted at greater and lower frequencies than would be expected based on their abundance alone. Spotted lanternflies are clearly selecting some species and avoiding others. Cyan colors indicate tree species where spotted lanternflies were never observed.

Photo: Jon Krupnick

References 

Dara, S. K., L. Barringer, and S. P. Arthurs (2015), Lycorma delicatula(Hemiptera: Fulgoridae): A New Invasive Pest in the United States, Journal of Integrated Pest Management, 6(1), 20, doi:10.1093/jipm/pmv021.

Kang, C., H. Moon, T. N. Sherratt, S.-I. Lee, and P. G. Jablonski (2016), Multiple lines of anti-predator defence in the spotted lanternfly,Lycorma delicatula(Hemiptera: Fulgoridae), Biological Journal of the Linnean Society, 120(1), 115–124, doi:10.1111/bij.12847.

Kim, J. G., E.-H. Lee, Y.-M. Seo, and N.-Y. Kim (2011), Cyclic Behavior of Lycorma delicatula (Insecta: Hemiptera: Fulgoridae) on Host Plants, Journal of Insect Behavior, 24(6), 423–435, doi:10.1007/s10905-011-9266-8.

Lee, D.-H., Y.-L. Park, and T. C. Leskey (2019), A review of biology and management of Lycorma delicatula (Hemiptera: Fulgoridae), an emerging global invasive species, Journal of Asia-Pacific Entomology, 22(2), 589–596, doi:10.1016/j.aspen.2019.03.004.

Liu, H. (2017), Biology and natural enemies of the spotted lanternfly,Lycorma delicatula,in North America, 2016 International Congress of Entomology, 30–32, doi:10.1603/ice.2016.109022.

Malek, R., J. M. Kaser, H. J. Broadley, J. Gould, M. Ciolli, G. Anfora, and K. A. Hoelmer (2019), Footprints and Ootheca of Lycorma delicatula Influence Host-Searching and -Acceptance of the Egg-Parasitoid Anastatus orientalis, Environmental Entomology, 48(6), 1270–1276, doi:10.1093/ee/nvz110.

Song, S., S. Kim, S. W. Kwon, S.-I. Lee, and P. G. Jablonski (2018), Defense sequestration associated with narrowing of diet and ontogenetic change to aposematic colours in the spotted lanternfly, Scientific Reports, 8(1), doi:10.1038/s41598-018-34946-y.

State of the Lehigh Experimental Forest, 2017

General ecology (EES-152) students have finished resurveying a portion of the Lehigh Experimental Forest, assessing changes in species mortality and recruitment since 2013. A total of 1174 trees were inventoried and measured from across the forest the last two years, representing more than 1/2 of all trees originally tagged in 2013. In the four  years since 2013, 167 of these 1174 trees have died (~14%) and only eleven new trees have established in the study area (<1%).  Data for the dominant tree species are shown in the plot below.

Abundance, mortality, recruitment, and the net percentage change of tree/shrub species in the Lehigh University Experimental Forest, 2013-2017. Relative frequency data are from 2013 (M. Spicer, MS thesis 2014) and indicate the percent of each species present (based on a total of 1174 trees). Total mortality and recruitment for each species with greater than 10 individuals are shown as percentages. Species are arranged from those undergoing substantial declines in abundance at the top to those that have increased in abundance on the bottom.

 

We will use these data to discuss processes controlling forest dynamics as the semester progresses.  However, for now, students should answer the following questions:

1. What factors might have caused the differences in mortality among species?
2. Develop a hypothesis to explain the lack of recruitment for most tree/shrub species. Then do some research on the two tree species that have successfully recruited and those species that have not. Are there species traits that are common to successful and unsuccessful recruiters? Are these traits consistent (or inconsistent) with what you might predict from your hypothesis?
3. What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? Assuming the rates of total tree recruitment and mortality are representative of future years, when will there be less than 100 trees in this forest?  In 2013, there were ~2000 trees in the forest so you can use that as your starting number. Show your work and describe how you arrived at your estimate.  Do you think this scenario is likely?  Why or why not?

State of the forest, 2016

General ecology (EES-152) students have finished resurveying a portion of the Lehigh Experimental Forest, with the goal of assessing changes in tree growth, mortality, and recruitment since 2013. A total of 690 trees were measured from across the forest, representing more than a 1/4 of all trees. In the three years since 2013, 70 of these 690 trees have died and only three new trees have established in the study area.  Data for the dominant tree species are shown in the plot below.

Tree abundance, mortality, recruitment, and growth rates in the Lehigh University Experimental Forest, 2013-2016. Relative frequency data are from 2013 (M. Spicer, MS thesis 2014) and indicate the percent of each species present (based on a total of 690 trees). Total mortality and recruitment across the time period are shown as percentages. The average increase in basal area of individuals of each species is shown, with the mean value for all species indicated with the vertical dashed line. Total change in basal area for each species, incorporating mortality losses and basal-area gains, is also shown.

We will use these data to discuss the processes controlling forest dynamics as the semester progresses.  However, for now, students should answer the following questions:

1. The dbh measurements were converted into estimates of area, assuming that each tree was a perfect circle in cross-section. Why do you think basal area was used to compare growth rates among the different species? Why was this expressed as the average change in basal area per tree? What factors might have caused the observed differences in radial growth among species?
2. What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? What factors might have caused the differences in mortality among species during these two years? What factors might be contributing to the lack of new tree recruitment in the forest?
3. Assuming the rates of total tree recruitment and mortality are representative of future years, when will there be no trees left in this forest?  In 2013, there were ~2000 trees in the forest. Show your work and describe how you arrived at your estimate.  Do you think it is likely that the trees will really be gone by this time?  Why or why not?
4. Which species had both very high mortality and very low growth during this time period? Do some research on current threats to this particular species, and summarize your research in a short paragraph.

Late night tree ID #ees152 @LehighEcology pic.twitter.com/vLIxRE14ba

— Oliver Rye (@OliRye) September 19, 2016

Great day in the forest with #ees152. pic.twitter.com/j2Tc9dv5Bg

— LehighEcology (@LehighEcology) September 12, 2016

Camera traps in the Lehigh Forest, Fall 2015

General ecology students installed two camera traps in the Lehigh University Experimental Forest.  The image tally after recording for about six weeks: one fox, one raccoon, one chipmunk, 2 domestic cats, 18 squirrels, and 38 deer.  Some highlights…

Female white-tailed deer searching for vegetation on Halloween.

A second female white-tailed deer rechecking the area.

Male white-tailed deer a few days earlier

“Fox went out on a chilly night…”

Rocky

Yes, you can see a black cat at night.

Must be some native vegetation back here somewhere.

A deer can’t live on Japanese Barberry alone.

Wow.

There has not been any tree recruitment here for decades.

Out for a noon-time stroll.  Looking for lunch.

Another picture of the same male.

An ecosystem modeller with the EES-80 class!

Still hungry.

Nope, no native birds here.

Not a very large forest fragment.

Time for a selfie.

Captured on the way to download the camera traps!

First resurvey of the Lehigh Experimental Forest

Growth, mortality, and recruitment (shown in red) of dominant tree species in the Lehigh Experimental Forest from 2013-2015. Average tree size and numbers of indivduals included in the survey shown in blue.

Taking inventory of the forest, 2015.

Students in general ecology (EES-152) resurveyed a portion of the Lehigh Experimental Forest, to assess changes in tree growth, mortality, and recruitment since 2013.  No new trees greater than 1.4 m high were documented, and both growth and mortality varied considerably among species.  Over 500 trees were measured, and the plot above shows data for the dominant trees (those with >15 individuals included in the survey).

We will use these data as a springboard for discussion of processes controlling forest dynamics, and will examine some of these issues in greater depth during our discussions and future lab activities.

 

For now, students should answer the following questions:

1. The dbh measurements were converted into estimates of area, assuming that each tree was a perfect circle in cross-section. Why do you think basal area was used to compare growth among the different species? Why was this expressed as the average change in basal area per tree, as opposed to the total change in basal area for all individuals of the species? What factors might have caused the observed differences in radial growth among species?

2.  What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? What factors might have caused the differences in mortality among species during these two years? What factors might be contributing to the lack of new tree recruitment in the forest?

3.  Which species had both very high mortality and very low growth during this time period? Do some research on current threats to this particular species, and summarize your research in a short paragraph.