Biological Control of Viburnum Leaf Beetle 2000
Principal Investigator: Paul A. Weston, Senior Research Associate, Department of Entomology, Cornell University, Ithaca, NY
Cooperators: Brian Eshenaur, Horticulture Extension Educator, Monroe Co. Coop. Ext., Rochester, NY;
Jana S. Lamboy, IPM Extension Educator, IPM Program, NYSAES, Geneva, NY
Viburnum leaf beetle, Pyrrhalta viburni (Paykull), is a relatively new landscape pest in New York State. It has been destroying susceptible viburnums in Rochester, NY, and has been steadily expanding its range since it was discovered in the state in 1996. As of this past summer, it has been found in 27 counties in New York, and was found for the first time in portions of Pennsylvania and Vermont that border New York. Given its rapid spread and the extent of damage observed to date, it seems likely that viburnum leaf beetle will soon pose a serious threat to viburnums throughout the Northeast and beyond.
The objective of this study was to evaluate the ability of several generalist predators and a pathogenic nematode for their ability to control viburnum leaf beetle in the laboratory. Such biological control agents are very desirable because they are non-toxic to humans and have little impact on beneficial insects, and are often self-propagating once applied. Thus, the major expense is likely to be the initial release of the biocontrol agent. In addition, such biological control agents would be very desirable for managing populations of viburnum leaf beetle in native landscapes, where pesticide applications would be very undesirable and impractical. Because viburnums in native landscapes likely foster the spread of viburnum leaf beetle, controlling the pest in these habitats might be a way to limit its spread.
Our experiments showed that two generalist predators (Harmonia axyridis, or the Asian multi-colored lady beetle, and Chrysoperla carnea, or green lacewing) were quite effective in killing larvae of viburnum leaf beetle in the laboratory. It is unclear how effective they would be in a field setting, but the results were encouraging enough to warrant such investigation in the future. Even more encouraging were the results with Heterorhabditis bacteriophora, a parasitic nematode; in most cases, the nematode killed all of the larval viburnum leaf beetles that entered the soil to pupate. This biocontrol agent appears to be effective enough that field trials should be conducted as soon as possible.
If any of these biological control agents are proven to be effective in the field, pesticides needed for controlling viburnum leaf beetle will greatly reduced. This will not only be of great benefit for growers of nursery plants, it will be of tremendous benefit to people who live in or frequent dwellings that are landscaped with susceptible viburnums being treated for viburnum leaf beetle; viburnums are used very extensively in landscaping, and many of them are susceptible to the pest. The cost of H. bacteriophora is fairly high if applications are made to small areas; at the recommended rate of 1 million nematodes per 50 square feet, the cost would be $2,000 per acre. There would no doubt be volume discounts for quantities this large. In cases were pesticide use is prohibited, however, such costs might be acceptable. Also, because biocontrol agents frequently are self-propagating, repeated applications may not be needed.