Fewer Spotted Lanternfly in Areas This Year as Compared to Last Year

Conversely, some areas are experiencing very high populations of SLF for the first time. Although the lesser numbers observed in some areas is encouraging, we are still very concerned about the potential harm SLF can cause to grapevines, the long-term health of important trees and our trade relationships with other areas. We believe several factors are at work, which are influencing spotted lanternfly (SLF) populations.

In some areas where fewer SLF nymphs were observed earlier in 2019, people have recently noted higher populations of adults than expected. The nymphs were most likely there all season long, but they were feeding in areas that were difficult to see, for example, high in the canopies of trees.

Currently, we do not have a good way to quantify the influence of any one of the factors discussed below, but researchers are interested in trying to develop methods to do that in the future.

People are killing SLF

Many people are working very hard to contain and control SLF populations. Residents of affected areas have been destroying egg masses in the winter months and killing nymphs and adults by swatting, using sticky bands and insecticides. The Pennsylvania and United States Departments of Agriculture (PDA and USDA) are reducing the numbers of one of the SLF's most favored host trees, Ailanthus altissima (Tree of Heaven) and establishing trap trees using systemic insecticides. This method has killed countless numbers of SLF. All these efforts have contributed to a reduction in the population.

Natural enemies of SLF are affecting their numbers

There are natural predators and parasites of SLF. From the beginning of the invasion, people have reported preying mantids, spiders, wheel bugs and other predaceous insects found eating SLF. These creatures are general predators, and they will catch and eat almost any insect they can. We don't know how much they are affecting the overall SLF population, but so far general predators do not seem to be making a big reduction.

Researchers at the Department of Conservation and Natural Resources and the USDA are studying other insects that parasitize SLF. The parasitic insects that have been discovered are very tiny wasps that lay their eggs on SLF. When the tiny wasp larvae hatch out, they feed on the SLF and kill it. There are several types of these tiny wasps, but so far, we do not know of any making a substantial reduction in SLF populations.

In 2017 and 2018, people began to discover SLF that were killed by naturally occurring fungi. A team of researchers from Cornell University and Penn State is studying these fungi to see if they might be used as an effective management method.

SLF will gather on individual trees over others

Researchers have looked at the anatomy of the mouthparts of SLF and believe that they are not strong at pulling sap into their bodies. The pressure of the sap within the vascular system of the tree might influence how easily SLF can acquire the sap they feed on. Even within a grouping of what appears to us to be all the same kind of tree, with comparable ages and health, SLF will congregate on certain individual trees. People have noticed that after large numbers of SLF feed on one tree for some time, they often relocate to other trees, perhaps to find a better meal elsewhere.

The populations of many insects follow a cyclic pattern. In some years there are high populations, and in other years there are lower populations. One example of this phenomenon is gypsy moth, another invasive insect in our area. In some years the populations of gypsy moth are high, and in other years the populations are low. This fluctuation is attributed to the influence of natural predators and parasites, and availability of good quality food, factors similar to what we believe we are seeing with SLF.

The fluctuations we are observing in SLF populations are not well understood at this time, but we might be starting to see the very beginning of a cyclic pattern of population peaks and valleys. Areas where populations are lower in 2019 might experience high populations again in the future.

It is important for everyone to remain vigilant, kill SLF when you can using safe, recommended practices, and do everything possible to avoid spreading them to new areas. The battle must continue!

For more information about the SLF, including management options, please visit Penn State Extension's Spotted Lanternfly website at or call 1-888-4BAD-FLY.