The quotes below are from Penn State Extension who along with the PA Department of Agriculture are at the forefront of the battle against SLF in Pennsylvania.
Also, don't be so sure what you see and believe is Tree of Heaven isn't Sumac. I made the same subsumption on my property until the Penn State Extension folks straightened me out.
"Adult Spotted Lanternflies begin emerging in early August. The female lanternflies are not reproductively mature at emergence. It is believed that they must feed on the Tree-of-Heaven (Ailanthus altissima) at some point in order to complete the life cycle. However, it is important to understand that the number of hosts on which the insect can complete its life cycle is unknown at this time.
Management strategies are needed to slow its spread to other regional fruit growing centers and to provide fruit growers with timely management tactics. This phloem-feeding Asian-native insect feeds upon over 65 species of plants and as such, is projected to become a serious pest of timber, ornamental trees, tree fruit orchards, grapes, stone fruit, and other small fruits such as blueberries. It can kill hops and feeds on several types of vegetables. SLF honeydew (sugary SLF excrement) and sooty mold (growing on honeydew) damage were found in vineyards in 2016, only two years after first detection.
In 2017, extensive sooty mold growth was observed on and around forest trees, such as tree of heaven, willow, and maples, and blackening of adjacent plants in the forest understory. Black walnut feeding caused yellowing and shocked trees into a general decline. SLF spread to more vineyards in 2017, reducing yield in one, and having as yet unknown long term effects on health of grapevines.
In late August, for the first time, large numbers of SLF were observed flying into and feeding on the trunks and branches of apple trees as well as nectarines and peaches. Immediate damage to tree fruit was not observed by the immigrating adults, but SLF egg cases found on the trees put the trees at risk for heavier and more sustained feeding by SLF nymphs and adults in Spring 2018. As an invasive pest in South Korea, SLF spread rapidly and caused significant wilting, dieback and mortality of grape vines and spread throughout the country in only 3 years".
