Common names: Viburnum Leaf Beetle
Scientific name: Pyrrhalta viburni (Paykull)
History: Viburnum leaf beetle (VLB) is native to Eurasia but appears to have become established in North America (Ottawa and Quebec) during the 1970's. VLB was first discovered in the United States in Maine in 1994, and as of 2007 was considered to be established west to Ohio as well as in British Columbia and Washington State. In 2009, VLB was discovered in Wisconsin (Dane County) and Illinois (Cook County).
Biology: VLB adults are present during mid-summer and consume Viburnum leaves. After mating, females implant eggs in small pits chewed into Viburnum twigs and cover the eggs with chewed wood. A single female may produce 500 eggs. The eggs overwinter and hatch into larvae in spring. Like adults, the larvae feed on Viburnum leaves. Initial defoliation is subtle with small larvae scraping away the outer surface of leaf tissue on the undersides of leaves. As larvae grow, defoliation becomes more obvious and leaves may have a "skeletonized" appearance (only leaf veins remain). Larvae eventually pupate in the soil before emerging as adults in June or July. Adult VLB create holes in Viburnum leaves that may cross leaf veins. One generation occurs per year.
Identification: Identification of VLB can be challenging as the adults and larvae appear similar to other leaf beetles. However, the presence of "skeletonizing" defoliation on Viburnum may be a good indicator of the presence of VLB. No insects native to Minnesota are known to skeletonize Viburnum, though the exotic Japanese beetle (Popilla japonica) may skeletonize Viburnum as adults. If skeletonizing-like damage is seen on Viburnum, look for the presence of larvae on or under leaves and / or egg pits on twigs – particularly new growth. If either of these life stages is present, then the insect is likely VLB.
Impacts: VLB feed only on Viburnum species. There are four species of Viburnum native to Minnesota (V. edule - squashberry, V. lentago - nannyberry, V. rafinesquianum – downy arrow-wood, V. trilobum – American high-bush cranberry), and one considered naturalized (V. opulus – European high-bush cranberry). Many more species of Viburnum are part of the horticultural trade and are present in landscape plantings throughout Minnesota. Viburnum species vary in their susceptibility to feeding by VLB, possibly due to differences in leaf morphology and chemistry. Exposure to sunlight also seems to affect susceptibility of individual plants to VLB with plants in shady locations being more susceptible than plants in sunny locations. A partial list of Viburnum species along with susceptibility ratings is available at the VLB Citizen Science Website.
Contact the Minnesota Department of Agriculture via Arrest the Pest if you suspect you have found viburnum leaf beetle.