NOVEMBER
2007

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

11-08-07

Some Lady Beetles Turn Out To Be Stinkers

Unlike insects in general, humans appreciate lady beetles. Sometimes called ladybird beetles or simply ladybugs, these little beetles are often bright red or orange-colored with black spots. Their color, polka-dot markings and even the name "lady" probably contribute to our positive attitude about these insects.

The main reason we humans place lady beetles on the positive side of our good-insect, bad-insect ledger is not because of their name or markings, it's because of their food habits. When it comes to eating, these insects are not very lady-like! They are voracious predators that feed on insects, including scales and aphids. Since scales and aphids feed on plants and are considered pests by farmers and gardeners, scale- and aphid-eaters like lady beetles are considered beneficial insects.

The name lady beetle goes back to the Middle Ages when farmers of the time prayed to the Virgin Mary for help with aphids feeding on the flax crop. When these beetles showed up to feed on the aphids, the farmers dubbed them beetles sent by Our Lady or Our Lady's Beetle. Today, we just called them lady beetles.

About 6,000 species of lady beetles have been identified in the world with about 400 species found in the U.S. Lady beetles are important biological control components of some insect control programs. One approach to this type of biological control has been to introduce a foreign species of lady beetle into the U.S. for the purpose of controlling a pest insect, such as an aphid or scale.

Over 170 lady beetle species have been introduced into the U.S. for biological control purposes and at least 26 have become established. The first such successful introduction occurred in 1888/1889 when entomologist C. V. Riley, head of the U.S. Department of Agriculture Entomology Division, coordinated the importation of the Vedalia lady beetle from Australia as a predator for control of the cottony cushion scale on grapes in California.

One of the latest introductions of a lady beetle to the U.S. was that of the multicolored Asian lady beetle. The beetle gets its name because it was originally found in Asia and varies in color, from bright red to tan, and in number of spots, from zero to 20.

The federal government made several attempts to establish the beetle to this country between 1960 and the mid 1980s. While the success of these attempts is unclear, what is clear is that, throughout the1990s, the beetle showed up across the eastern U.S. and parts of Canada. Some scientists suggest that this species of lady beetle might have originated from an accidental introduction on a freighter from Japan through the port of New Orleans.

While the Asian lady beetle is beneficial in the field because it feeds on pest insects, it has become a problem for homeowners. This lady beetle likes to spend the winter months in our homes. Native lady beetles can also show up in our homes during the winter but, for the most part, just spend the cold months under leaf litter in the woods.

In addition to just being a nuisance all winter, the Asian lady beetle also is a little stinker. While not very ladylike, it seems all lady beetles can release an odorous, distasteful fluid from their leg joints. The process is called reflex bleeding, and it serves to help prevent the lady beetle from becoming a meal for some other creature. If you happen to get the fluid in your mouth, you can understand why it is effective in preventing the insect from becoming a meal.

These beetles also like to ingest fermenting juices found in ripe fruits. So they can be found feeding on raspberries, apples and grapes. So an Asian lady beetle or two crushed in the wine press along with the grapes can taint the wine.

This lady beetle spends the winter in our homes, feeds on ripe fruits, contaminates wine and produces stinky spots on linens and curtains. And, to add insult to injury, will bite when it gets the chance. In every family, there is a stinker or two, even among lady beetles!   

 

Writer: Tom Turpin
Editor: Olivia Maddox