ASIAN LADY BEETLE
When USDA’s (United States Department of Agriculture) entomologists decided to introduce the Asian lady beetle for biological control of pecan aphids in 1965 in California, affecting vineyards and spoiling millions of litres wine in Ontario did not even enter their minds.
The multicoloured Asian lady beetle (Harmonia axyridis) 6 mm in length and 5 mm in width likes to inhabit soybean fields, and once the crop is harvested settles in nearby vineyards and in their absence in homes. Over time, it spread eastward and in the absence of vineyards entered homes, eventually arriving in the Niagara Peninsula.
Soybeans are harvested a few weeks earlier than grapes and once the crop disappears, these beetles take refuge in nearby vineyards. They like the sweet juice of grapes particularly of Vitis vinifera family fruit. According to researchers the Asian lady beetle is less interested in hybrid grapes because of their methylantrinilate flavour and interestingly enough hybrid grape wines like Baco Noir and Vidal tolerate much higher concentrations of the yellow secretion they emit when scared. Asian lady beetle’s yellow secretion that causes wines to smell like peanuts is extremely potent and an infinitesimally small quantity can ruin thousands of litres of wine.
In 2001, several Ontario wineries had to dispose a million litres of infected wine. Some tasters can detect Asian lady beetle infected wine that contains two part per trillion, the threshold is five part per trillion. An infected wine smells strongly of peanuts which many but not all consumers find objectionable. Infected wines do not represent a health hazard. Hybrid wines can contain up to 25 parts per trillion and not smell of peanuts. Surprisingly Sauvignon Blanc can contain up to 40 parts per trillion and smells, as it should naturally. Researchers have yet to determine the reasons for Sauvignon Bancs ability to tolerate much higher levels of pyrazine without smelling offensive.
One solution to avoid Asian lady beetle infection is to hand harvest and employ sorting tables to inspect each bunch of grape before crushing – a cost many if not most wineries can ill afford.
Article contributed by Hrayr Berberoglu, a Professor Emeritus of Hospitality and Tourism Management specializing in Food and Beverage. Books by H. Berberoglu