Wine Grapes in the Midwest: Reducing the Risk of the Multicolored Asian Lady Beetle

Wine grape production has increased significantly in Minnesota and other Midwestern states during the past 20 years. Even though the acreage of Minnesota grapes is low (about 220 ac.), the high value of the crop, ranging from $4,000 to $7,000/ac, depending on the grape variety, has increased its importance in Minnesota and enhanced the diversity of agriculture and the economy. This growth in the wine industry has been attributed to the releases of new wine grape varieties, such as Frontenac and La Crescent, which are more winter hardy, tolerating temperatures as low as -30 °F. These varieties also are resistant to plant diseases such as downy mildew and powdery mildew. In the past, Minnesota and surrounding states had not typically experienced problems with any particular insect pest, but in 2001, wine makers began to notice a foul taste in their wines. The new taste resembled “burnt peanut butter” and later it was found to be associated with the presence of the multicolored Asian lady beetle (MALB), Harmonia axyridis, which was found in the clusters during harvest and wine processing. Since then, MALB has become an economically significant contaminant pest of the winemaking process. The beetles tend to aggregate on clusters just before harvest, and subsequently, some beetles may be incorporated with the grapes during wine processing. Once crushed, MALB releases their foul smelling hemolymph (insect blood) that can taint the flavor and aroma of the resulting wine. Tainted wine and the unacceptable taste associated with it has caused millions of dollars in losses (unpublished data) to the wine industry throughout the Eastern U.S. and Southern Canada. Even though MALB can be observed in vineyards throughout the growing season, control measures are not justified until 1-2 weeks before harvest. There are three reasons why grape growers should not manage MALB earlier in the season. First, this insect cannot directly damage, or penetrate grape skins. To date, MALB have only fed on berries that have been previously damaged by other insects, birds, diseases, or “splitting.” Although berries can be damaged as early as the berry set stage, damage increases dramatically as the sugar content rises over the last few weeks of ripening. Second, MALB is a contaminant pest and its presence in the vineyard throughout the growing season does not affect grape yield. Finally, MALB is one the most abundant predators of several insect pests, including pests of grapes, and in several other crops (e.g., soybeans, sweet corn), where they may further contribute to reducing insect pest populations.