Why am I seeing more spotted lanternflies? Lycorma delicatula

This week we turn to the Bug of the Week mailbag to explore why some folks are seeing more spotted lanternflies (SLF) around their homes and in their landscapes.

Reason 1. Since first detected in the US almost a decade ago, SLF has made an astounding range expansion from their entry point in Berks County, Pennsylvania to Huntington County, Indiana more than 580 miles away. This feat was not accomplished on their own. SLF are believed to move only a matter of several miles by walking, hopping, and flying. Nope, these vagabonds are super stowaways and heinous hitch hikers, moving as eggs, nymphs, and adults on vehicles, lawn furniture, plants, and other natural and human-made objects. Here in the DMV and adjacent states like Delaware, Pennsylvania, and New Jersey, they made beachheads and rapidly colonized several counties. All counties in New Jersey and Delaware house breeding populations, with Maryland not far behind. Larger states like Pennsylvania and Virginia still have uninfested counties but one look at Figure 1 suggests that these states are trending toward full saturation. Bug of the Week’s outdoor SLF tracking site near Antietam Battlefield in Maryland discovered a couple dozen SLF adults in 2022. Last week hundreds of adults festooned branches and trunks of trees. Dramatic population explosions are underway in several landscapes in the DMV and in some 14 states in eastern North America with new detections of infestations being reported on a weekly basis. So yes, due to range expansion there are indeed more lanternflies to be seen today in the US than there were just a few years ago.

Reason 2. The second and perhaps more salient reason why there seem to be more SLF has to do with their seasonal phenology, that is the regular progression of development, survival, and activity throughout the year. In a previous episode in early May, we met tiny SLF nymphs as they hatched from eggs that survived winter’s onslaughts. Shortly after hatch, active feeding stages of spotted lanternfly were at their peak. Since early May, local populations of SLF dramatically declined as lethal weather events like cold and rain, murderous predators like spiders, mantises, and assassin bugs, diseases caused by fungi, and pesticide applications have taken their toll. The illusion that there are now more SLF than there were a few months ago has two explanations. First and foremost is the fact that adult SLF are roughly 10 times larger in size than tiny hatchling nymphs. Bigger bugs are easier to see. Second, these adult rascals are on the move, taking wing and winding up on the side of a house, on a sidewalk, lawn chair, or favored tree. While young, SLF nymphs feed on a wide variety of trees, shrubs, and herbaceous plants, more than 70 species of host plants are known. Nymphs are widely distributed in the landscape. Adults are most frequently found on a smaller sample of trees with invasive tree of heaven high on the list, and maples, walnuts, and a few others also commonly mobbed. Highly mobile adults and hordes of sap-sucking adults create a mien of many more lanternflies.

As we enter the period of adult migration, feeding, honeydew production, grape vine ravaging, and general annoyance, people will be wondering what to do. One popular and highly touted tactic is to do a little tap dance on SLF adults stranded on sidewalks or on the ground. The logic here is that every other SLF killed will be one less to lay eggs. Oh, every other bug because only females lay eggs and the sex ratio is likely 50:50, get it? Unfortunately, in the early stages of the SLF invasion, some 1.5 million SLF were killed by noble volunteers in Berks and nearby counties, yet these scoundrels managed to spread to surrounding counties and states more than 500 miles away. The contribution of stomping and squishing to reductions in SLF populations remains a mystery. Nonetheless, as Sheryl Crow opined, “if it makes you happy, it can’t be that bad”, so squish away if it makes you happy.

In April and May when millions of spotted lanternflies hatched, this year’s crop of lanternflies was at its zenith. As tiny black and white nymphs dispersed, they fed on myriad herbaceous and woody plants. Their colors changed from black and white to red, black, and white as they developed. Their numbers dramatically declined as weather, beneficial insects and diseases, and human interventions took their toll. Although fewer survived, when large adults gather to feed on favored trees or land on humans and buildings, their presence will be observed by more people. Many will perish on sidewalks and roads beneath the tires of vehicles and feet of humans.

What’s the bright spot here? Well, my tree care guys, certified arborists near ground zero in Pennsylvania, report that SLF populations have declined noticeably since the early years of the invasion in the late 20-teens. How so? Well, the aforementioned push-back by Mother Nature’s hit squad of predators, parasitoids, and pathogens coupled with host plant removal and highly efficacious and well-timed insecticide applications all help mitigate problems created by SLF. Quarantines enacted by several states appear to be slowing the spread of SLF on a regional scale. Let’s hope that the combined efforts of Mother Nature and clever humans can help keep this nocent invader at bay.

Acknowledgements

Bug of the Week thanks members of the Penn-Dell and Mid-Atlantic chapters of the International Society of Arboriculture for providing the inspiration for this episode and Dr. Shrewsbury for spotting and wrangling spotted lanternflies. We acknowledge the great work of scientists contributing to our knowledge of this pest with particular thanks to authors of articles and aforementioned websites used as references, including “Perspective: shedding light on spotted lanternfly impacts in the USA” by Julie M. Urban, “Dispersal of Lycorma delicatula (Hemiptera: Fulgoridae) Nymphs Through Contiguous, Deciduous Forest” by Joseph A. Keller, Anne E. Johnson, Osariyekemwen Uyi, Sarah Wurzbacher, David Long, and Kelli Hoover, “The Establishment Risk of Lycorma delicatula (Hemiptera: Fulgoridae) in the United States and Globally” by Tewodros T. Wakie, Lisa G. Neven, Wee L. Yee, and Zhaozhi Lu, and “Applications of Beauveria bassiana (Hypocreales: Cordycipitaceae) to Control Populations of Spotted Lanternfly (Hemiptera: Fulgoridae), in Semi-Natural Landscapes and on Grapevines” by Eric H. Clifton, Ann E. Hajek, Nina E. Jenkins, Richard T. Roush, John P. Rost, and David J. Biddinger. Thanks to Brian Eshenaur and the entire team at the New York State Integrated Pest Management Program of Cornell University for providing the updated maps of spotted lanternfly in the US.

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