Article By: Harvey Finkel, MD
Ladybugs, now becoming a threat to our wine supply, were commonplace when I was a small boy in Brooklyn, even in that urban setting. We naively called them "potato bugs". I don't know why. They congregated on the large leaves of the small trees we called, with perfect logic, "potato-bug trees". The bugs were considered harmless, even vaguely lucky, by the cognoscenti among us. When abused, the bugs would emit a pungent-smelling droplet of liquid. The small boys and smaller bugs, being abstinent, were unconcerned with wine odors and tastes. But, now grown up, the boys are beginning to worry.
This same pungent liquid is increasingly tainting wine. Remarkably small doses can render a wine impalatable, imparting vegetal (peanut, bell pepper, asparagus) and earthy and herbaceous smells and tastes as well as increased sourness and bitterness. Floral and fruity qualities are damped. Red wine may be slightly more affected than white. I wonder whether some bottles called corky might really be ladybugged. Much of the elucidation of this problem has been done at Brock University, St. Catharines, Ontario, by a team headed by Gary Pickering, chair of the Department of Biological Sciences. The group's research has been reported since 2OO4 in a series of scientific papers in the journal of enology and viticulture, journal of food science, international journal of food science and technology, and vitis.
The particular species of ladybug of chief concern, known with more dignity as the Multicolored Asian Lady Beetle, is Harmonia axyridis. It is also called Harlequin Lady Beetle, because of color variation, and Halloween Lady Beetle, because the promiscuously unladylike rascals, male and female, swarm in late October just before hibernation. (The males are no doubt called "girlie bugs" by a certain western governor.) Ladybugs are more genteelly called "ladybirds" by the British. The "lady" is short for "Our Lady's", a mark of the esteem in which the critter was held. A related species of ladybug is the official state insect of Ohio.
Asian Ladybugs, which like to dine on aphids and scale insects and their eggs (for breakfast, I suppose), were imported from northeastern Asia (Japan, Korea, Siberia) by the US Department of Agriculture on several occasions since the early twentieth century to control these pests, but with indifferent results. During the past few years, however, the bugs have proliferated, perhaps enhanced by the availability of soybean aphids, a delicacy that migrated from China. Asian ladybugs have appeared throughout the US and Canada, and now in Europe as well. Their presence is no longer viewed sanguinely. They may be attracted to bruised, ripe fruit, especially in vineyards in the vicinity of soybean fields.
When stressed, as, for example, when caught in a crusher/stemmer, our ladybugs respond by reflexly bleeding from their leg joints a hemolymph (the bugs' equivalent of blood) that contains highly potent volatile compounds, especially 2-isopropyl-3-methoxypyrazine (sure looks potent), known more fondly as IPMP, or ladybug taint. The Multicolored Asian Lady Beetle's hemolymph contains IPMP in much higher concentration than that of other ladybug species. As I learned long ago in Brooklyn, this is strong stuff. It takes less than a billionth of a gram per liter of wine for the taint to be detectible, or the product of one enraged bug per eleven pounds (five kilograms) of grapes. Individuals vary in their ability to sense the taint, much like most odors and tastes. Other than its unpleasantness, the taint is harmless, to health, that is, but important financial losses ensue for wine producers.
The presence of ladybugs on the grapes before the crush does not cause the wine to be tainted. Any method of bug removal should be gentle. Methoxypyrazines are normally present in various vegetables and in some grapes, notably sauvignon blanc and the cabernets, where just a touch contributes to varietal character, but excess, as in the unripe fruit of too-cold vineyards, leads to green, vegetal flavors.
The Pickering group at Brock has been of late evaluating remedial treatments for tainted wine. They found that, except for the the displeasing organoleptics, the chemical structure and composition of affected wines are otherwise unaltered. Bottle aging does not help. Tainted wines were treated in a controlled manner with bentonite, activated charcoal, oak chips, deodorized oak chips, and ultraviolet light (red wine) or visible light (white wine). Activated charcoal reduces the concentration of IPMP in white wine, but not the sensed taint - puzzling. Oak chips, but not deodorized oak chips, reduce the intensity of the taint in white and red wines, especially the asparagus component, without reducing IPMP. It is thought that oak simply masks the taint. Deodorized oak appears to enhance asparagus odor in white wine, without affecting IPMP - also puzzling. Deodorized oak chips reduce IPMP in red wine. Other treatments have no or limited effect. Overall, none of the treatments is ready for prime time.
The search continues, however, now focused on a protein with high affinity for methoxypyrazines. It is hoped this protein will bind the taint-causing compounds, and, used as a fining agent, eliminate them. Don't expect satisfaction tomorrow, for there are obstacles to overcome in getting this scheme to work.