Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management



AUTHOR

Andy Allen
University of Missouri
Division of Plant Sciences
(573) 882-6752
allenra@missouri.edu

Multi-Colored Asian Lady Beetle Taint in Wine

Andy Allen
University of Missouri
(573) 882-6752
allenra@missouri.edu

Published: August 15, 2011

Sometimes good ideas have downsides. It's called the Law of Unintended Consequences. Such is the case with Multi-colored Asian Lady Beetle. A species of lady beetle native to an area in Asia from southern Siberia to southern China, the Multi-colored Asian Lady Beetle (MALB) was introduced into the United States on several different occasions during the course of the Twentieth Century in an attempt to provide natural control of soft-bodied insect pests of crops, particularly aphids. The earliest known introduction was into California in 1916. But it was its introduction into areas of the eastern U.S. in the late 1970's and early 80's that led to established populations across most of the continental US. (Note: there is some speculation that it was not the intentional release of MALB, but accidental introductions through seaports that led to established populations in the U.S.) The MALB is a very successful predator and was introduced to provide biological control of pecan aphids in the southeastern U.S.; a job that it has performed very well. As it has become established and spread across the country it has also helped provide biological control of aphids and other softbodied pests in crops such as apples, citrus, alfalfa, sweet corn, cotton, tobacco, and winter wheat. In the Midwest, it is well known for its predation of soybean aphids. But with its success has come an unintended consequence: it has become a nuisance pest in some other crops, particularly winegrapes in the Eastern and Midwestern U.S. and Ontario.

In the latter part of the fall season, in areas where large populations of MALB and vineyards coexist, the beetles will move into the vineyards and take shelter within the grape clusters. This may be due to the declining populations of insect-prey in the late fall or the beetles may be seeking sugars and other carbohydrates from the berries themselves before hibernating. Despite some contradictory research results, the MALB does not appear to be a direct pest of winegrapes in that they do not attack or feed on undamaged berries. So, they do not cause yield loss. They do however, feed on already damaged fruit and this damaged fruit may in fact attract them. But, the real problem with MALB and winegrapes is that the MALB contain a substance in their hemolymph that causes "off" odors and flavors when incorporated into the wine made from grapes in which the MALB have been residing. This substance, 2-isopropyl-3-methoxypyrazine (IPMP), causes peanut, bell pepper, asparagus, and earthy/herbaceous aromas and flavors in wines and can mask or reduce the varietal fruit characteristics of the wine. The IPMP is released either through "reflex bleeding", a defensive mechanism when the beetles are stressed or when they are crushed at the winery along with the grape clusters. Making matters worse, it takes very few MALB to produce a noticeable fault in the wine, referred to Lady Bug Taint (LBT). While estimates vary, most sources agree that 1 MALB per pound of grapes produces a taint noticeable by even casual wine drinkers, while winemakers, wine connoisseurs, trained sensory panels, and those with well-developed senses of smell and taste can detect LBT at contamination levels of 1-2 MALB per harvest lug (approx. 30 pounds of grapes). The sensory level can be affected by the variety of grape, with neutral-aroma/flavor wines such as Chardonnay having a lower threshold of detection than a highly aromatic/ flavored wine such as Riesling. Indeed, trained sensory panelists were able to detect LBT at a level of 0.318 ng/L of Chardonnay wine, or 0.3 parts per trillion. For Riesling, the level necessary for detection by the panel was 2.3 ng/L. Several winemaking practices have been tested to try to ameliorate LBT in wine, but most are ineffective or only reduce the taint but not remove it. And unfortunately, IPMP is a very stable compound, so it doesn't degrade in the wine over time. Research showed that wines made by adding MALB during the winemaking process and then bottled and aged 10 months had aroma and flavor profiles similar to newly-made LBT-contaminated wines.

MALB look like most native lady beetles. Their color can range from tan to yellow to orange to red. Their wing covers can have from 0 to 19 black spots on them. But MALB can be identified by a characteristic "M" (or "W", depending on which end you're looking from) on their pronotum, the region behind their heads. In Missouri, MALB can be found in small numbers in vineyards throughout most of the growing season preying on other insects, but do not appear in large numbers in the vineyard until late in the fall when most of the winegrape harvest is over. However, Norton winegrapes and blocks of certain varieties left to ripen to the point of shriveling that are used to make what are called "late-harvest" wines are at risk of LBT from Multi-colored Asian Lady Beetles.

This still represents a very substantial percentage of the winegrape acreage in the state. Since the use of remedial actions in the winemaking process has little effect, this means that the best method to avoid LBT in wines is to avoid harvesting MALB along with the grapes. Recently, several insecticides have been labeled specifically for the control of MALB in winegrapes. These include Belay 2.13SC, Clutch 50WG, Venom 70SG and Scorpion 35S. Belay and Clutch have a 0-day preharvest interval (PHI) while Venom and Scorpion have a 1-day PHI. The best strategy is to apply insecticides in time to not only kill the MALB but for them to fall out of the clusters, as dead MALB may still have the capability to taint wine. In all cases, read the label of the material used for restrictions and recommendations on use.

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REVISED: September 28, 2011