Pest Watch: Viburnum Leaf Beetle

Pest Watch: Viburnum Leaf Beetle

FS202E
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Todd Murray, Associate Professor, WSU Extension Pullman, Eric LaGasa, Entomologist (retired), Washington State Department of Agriculture, Chris Looney, Ph.D., Entomologist, Washington State Department of Agriculture, Nick Aflitto, Administrative Professional, WSU Extension

Viburnum leaf beetle (Pyrrhalta viburni) is an invasive pest from Europe that is spreading in Washington State. It can cause branch dieback and even death of Viburnum species, including native species and popular ornamentals.

This publication describes how to identify viburnum leaf beetle and gives numerous resources for home gardeners and landscape professionals to use when they are dealing with this pest.

If viburnum leaf beetle is found outside its reported range of Whatcom, Skagit, Snohomish, and King Counties in Washington State, please report these new finds to the authors or your local Extension office.

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Introduction

The viburnum leaf beetle (Pyrrhalta viburni) is an invasive pest from Europe that is currently established in the eastern United States, British Columbia, and parts of Washington. The beetle’s wide distribution, particularly in western North America, increases the likelihood of this pest expanding its range in the Pacific Northwest.

Heavy infestations can cause branch dieback and death of several Viburnum plant species including native species and popular ornamentals found in home landscapes. The purpose of this factsheet is to educate landscape professionals, nurseries, and home gardeners about the occurrence of this new pest.

Distribution

Viburnum leaf beetle (VLB) was introduced from Europe to North America sometime in the early 1890s. The earliest recorded collections in North America are from 1924, in Nova Scotia, Canada, although there is no evidence that these were from reproducing populations (Weston et al. 2007). The beetle became established in and around Ottawa, Ontario, in the late 1970s, and was first recorded in the United States in Maine, in 1994.

VLB has since spread to neighboring states, including New York, Connecticut, New Hampshire, Massachusetts, Vermont, and Pennsylvania (Weston et al. 2007). The beetle has also spread into several midwestern states, with recent finds in Ohio, Michigan, Wisconsin, and Illinois (NAPIS 2015).

In 2001, gardeners in British Columbia found VLB on southern Victoria Island and in the Fraser Valley (Hueppelsheuser 2010). It quickly spread southward into Washington State. In 2004, VLB samples from a homeowner north of Bellingham were confirmed at the Washington State University Whatcom County Extension Master Gardener Clinic. Further survey found VLB throughout Whatcom County; the beetle was detected in northern King County in 2015.

If the pest is found beyond its reported range of Whatcom, Skagit, Snohomish, and King Counties in Washington State, please report these new finds to the authors or your local Extension office.

Identification and Life Cycle

In the Pacific Northwest region, VLB has one generation per year and overwinters as eggs. Overwintering eggs are found in protective wounds along the twigs of last year’s growth. Eggs hatch in spring and the small larvae begin to feed on the foliage. Often, egg-hatch is timed with the unfolding of the host plant’s leaves in spring. The newly hatched larvae are very small (about 1/16 inch long) and greenish-yellow (Figure 1).

Figure 1. Early instars and feeding damage to viburnum of VLB larvae in the spring. Photo by Todd Murray.
Initially, small larvae graze on the undersurface of the leaf between leaf veins, removing the soft leaf tissue. As feeding continues, the larvae grow and begin to darken in color. A pattern of dark spots will also begin to appear on each larva as it matures (Figure 2).

There is a characteristic habit to the larval feeding where the foliage is consumed between the leaf veins, leaving only a skeletonized leaf when feeding is complete (Figure 3).

The mature larvae will reach 1/2 inch in size and crawl down the host plant to pupate in the soil. Larvae construct a pupal cell from soil particles and bodily secretions within the first inch of soil (Weston and Desurmont 2008). The pupal stage typically lasts two to three weeks, ending with the emergence of an adult beetle from the soil. Adults are 1/4 to 3/8 inches long and are bronze to brown in color with filamentous antennae (Figure 4).

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Copyright 2016 Washington State University

Published April, 2016

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