Viburnum Leaf Beetle – Pyrrhalta viburni

The viburnum leaf beetle, Pyrrhalta viburni, is a small brown insect native to Eurasia that was accidentally introduced into North America during the early 1900s. It was first detected in the U.S. in 1994, and has been rapidly expanding its range ever since. It is now (Sept. 2008) found throughout New England, all of New York state and into western Pennsylvania, Ohio and Michigan. A separate invasion is taking place in the Pacific Northwest. [3]
June 5, 2015 Chicago Botanic Garden officials reported the VLB has been spotted at the 385-acre facility at Glencoe, Illinois, for the first time in its 43-year history. Hundreds of leaf-munching larvae were discovered at two locations in the park, demonstrating this destructive pest’s spread westward [5].

Both the adult and larval stages are voracious eaters that can defoliate viburnum shrubs entirely. Plants may die after two or three years of heavy infestation. The most susceptible species of Viburnum happens to be Viburnum dentatum, commonly known as arrowwood.

Viburnum leaf beetles only infest viburnums. They complete just one life cycle each year. Adult females lay up to 500 eggs on viburnum twigs in summer and early fall. The eggs overwinter and hatch in spring. Larvae feed on foliage until early summer, then crawl down the shrub and pupate in the soil. Adults emerge from the soil in midsummer, feed again on viburnum foliage, and mate. Egg hatch to adult takes just 8 to 10 weeks. [4]Live adult leaf beetle photographed near Marienville, PA, reflecting a continuing spread westward.
Leaf beetles feed strictly on plant materials. The adults usually consume leaves, stems, flowers, and pollen. Most larvae are subterranean in habit, feeding on roots and rootlets, but others will consume foliage as well. Many chrysomelids are very specific to particular host plants, but most are able to live on a variety of plants; i.e. the so-called dogbane leaf beetle, Chrysochus auratus, which feeds on prairie plants such as milkweed (Asclepias sp.) and plants in dogbane genus Apocynum. [2]
References

1. JR, Ross H. Arnett et al., “American Beetles, Volume II: Polyphaga: Scarabaeoidea through Curculionoidea,”
2. Jergen Gross, “On the Evolution of Host Plant Specialization in Leaf Beetles” (Logos, 2001)
3. Paul A. Weston and Victoria Nuzzo, Cornell University, “The Impact of Viburnum Leaf Beetle on Native Arrowwood“
4. Cornell University, Department of Horticulture, “Viburnum Leaf Beetle Citizen Science“
5. Chicago Tribune, June 5, 2015, “‘New bug in town’ at Chicago Botanic Garden targets viburnums“

Tree Encyclopedia / North American Insects & SpidersOnline since 2002