Previous episodes of Bug of the Week contemplated nefarious exotic invaders including the Brown Marmorated Stink Bug, Asian Tiger Mosquito, and Emerald Ash Borer. This week we visit an alien of lesser repute, Pryeria sinica. This saga begins with Euonymus, a genus of landscapes plants widely used as shrubs and ground covers.
Back in 2002, a new pest was discovered in Fairfax, VA, when a homeowner noticed voracious caterpillars munching her ornamental euonymus. Caterpillars were sent to Eric Day at the Insect Identification Laboratory in Blacksburg, VA. Eric reared out the larvae and sent the unknown adult moths that emerged to specialist John Brown at the Systematic Entomology Laboratory at USDA. Dr. Brown identified the moth as one not known to occur in the US – a new exotic invader. The scientific name of this alien is Pryeria sinica. Prior to its discovery in Fairfax, this perfidious moth was only known from eastern Russia, China, Korea, Japan, and Taiwan. In 2003, more moths were collected in Northern Virginia and on May 28, 2003, Gaye Williams at the Maryland Department of Agriculture identified specimens of Pryeria sinica from Anne Arundel County, Maryland. Somewhere along the way, the new pest was dubbed the euonymus leaf notcher due to its propensity to munch the margins of leaves, creating a distinctive pattern of destruction
The leaf notcher passes winter as taupe colored eggs deposited in clusters or 150 or more on pencil-sized twigs near terminals of branches. Eggs hatch in mid-March most years, but in this unseasonably warm year, the caterpillars arrived in early March. Tiny caterpillars first feed in tight silken webs spun around unfolded leaves at terminals of branches. As larvae grow, they move to expanded leaves to feed and are often found in large groups. Their presence is easily recognized by marginal notches along the edge of leaves, and by coarsely shredded leaves. When abundant, these leaf-eating dynamos can entirely strip shrubs! After completing development, larvae wander from the plant seeking protected locations to pupate. Large numbers of wandering caterpillars may alarm homeowners, but citizens should remain calm as the caterpillars are not known to eat humans or pets. The caterpillars spin cocoons amid fallen leaves and adult moths appear in the autumn to fly, mate, and lay eggs on the terminals of euonymus branches.
Unlike many moths, these are day fliers. Unique patterns and colors on the body and wings of the moths give them a striking resemblance to wasps. The fact that they mimic wasps may help them avoid being eaten by day-feeding predators such as birds. In North America, the leaf notcher has been reported on Euonymus japonicus and E. kiautschovicus ‘Manhattan’. In its native range in Asia, the pest has been reported feeding on E. sieboldianus, E. japonicus, and E. alatus. Moreover, other members of the Celastraceae family, such as Celastrus punctatus and C. orbiculatus are also recorded as hosts for this pest. Euonymus leaf notcher has two obvious weak points that provide excellent opportunities for management. From the time that egg laying ends in December until eggs hatch in spring, careful inspection will reveal eggs, which are then easily crushed or simply removed by pruning out infested terminals. Later in the spring when small larvae aggregate on localized twigs of a plant, they too may be removed by a gloved hand or pruner. If larvae are widely distributed, abundant, or otherwise difficult to control manually, then several insecticides perform well in eliminating these rascals. Some of the most “environmentally friendly” insecticides for killing caterpillars contain derivatives of the soil microbe Bacillus thuringiensis kurstaki. These insecticides kill by destroying cells in the gut of the caterpillar – a slow and painful death to be sure, but one that does not affect other kinds of insects or animals. Another excellent caterpillar annihilator contains the active ingredient spinosad, one of the EPA’s reduced risk insecticides.
Euonymus leaf notcher, where are you now? From its original detection sites in Anne Arundel County in Severna Park, Glen Burnie, and Millersville, the notchers have expanded their range to Annapolis, Bowie, and Linthicum. They are knocking on the doors of Howard and Baltimore counties. If you find the euonymus leaf notcher or suspect that you have, you can contact Mike Raupp, email@example.com, 301-405-8478; or Dick Bean, Maryland Department of Agriculture, firstname.lastname@example.org, 410-841-5920 for finds in Maryland. In Virginia, contact Eric Day, email@example.com, 540-231-4899. You can also contact your friends at the Cooperative Extension Service in your county in either state.