WOOSTER, Ohio - It isn't enough that homeowners must battle to keep the multicolored Asian lady beetle out of their homes, now Ohio fruit growers must contend with another one of the insect's behavioral quirks: an insatiable appetite for sugar.
Ohio State University entomologists have documented large numbers of Asian lady beetles feeding on peaches, grapes and apples, but whether the damage found on the crops is caused primarily by the insect, or by another host has yet to be determined.
"We've heard from field reports that 25 percent of some of the peach crop was damaged this season due to something nibbling on the fruit. Originally we thought it might be grasshoppers," said Kovach. "Then we started finding large numbers of lady beetles aggregating on damaged and undamaged fruit and are questioning whether they could do this type of damage." The multicolored Asian lady beetle, though considered a pest because it tends to hone in on homes as overwintering sites, does have beneficial characteristics in that it feeds on aphids, scale insects and other agricultural pests. Its diet restriction of insects, however, is what makes the lady beetle's craving for nectar rather unusual.
"There is some unique behavioral shift going on that we don't understand yet that is causing the lady beetle to change its feeding preferences," said Kovach. "Between about September 1st and October when it heads off to find overwintering sites, there is a drop-off in aphid feeding and the insect's attraction to black light traps. They are interested in neither and seem to be going for the fruit." If researchers' speculations hold true, the news won't bode well for fruit growers. "Peaches and grapes are at a greater risk because their soft skin is easily damaged," said Kovach. "In grapes, it could really be a problem because people are detecting the chemical smell from the beetles in wine." The short time window that the lady beetles aggregate on the fruit is also a dilemma for growers who spray their orchards. "There are restrictions on certain pesticides that require one to wait several days after spraying before the fruit can be harvested," said Kovach. "We are currently looking at several chemicals that have a shorter life that could be applied within this time window." He also mentioned the possibility of growing early-developing cultivars to avoid the overlap of fruit ripening and the lady beetle's sugar interest.
Apples, peaches and grapes rank among the top commodity crops grown in Ohio. According to the 2000 Ohio Department of Agriculture and Ohio Agricultural Statistics annual report, Ohio growers harvested 85 million pounds of apples, valued at nearly $20 million; 9 million pounds of peaches, valued at $4 million; and 7,000 tons of grapes, valued at $2.5 million. Apple production in Ohio is ranked 10th in the nation; grape production is ranked eighth; peach production is ranked 18th.