PEST BIOLOGY, ECOLOGY, AND INTEGRATED PEST MANAGEMENT FOR SUSTAINABLE AGRICULTURE
Location: North Central Agricultural Research Laboratory
Title: What's Buggin' You
Submitted to: Brookings Register
Publication Type: Popular Publication
Publication Acceptance Date: October 18, 2006
Publication Date: October 18, 2006
Citation: Hesler, L.S. 2006. What's Buggin' You. Brookings Register. Brookings, South Dakota. October 18, 2006. pp. A1, A5.
Recent establishment of an exotic insect known as the multicolored Asian lady beetle in North America threatens to tarnish the good reputation of a generally beneficial group of insects. Lady beetles, commonly called ladybugs, are one of the favorite and most widely recognized kind of insects. They are often depicted favorably in children's books, fables, and nursery rhymes. Some catch the fancy of artists due to black spots and bands that contrast with vivid red or orange forewings, though many lady beetles are dark with few or no markings. More importantly, lady beetles are beneficial because they provide biological pest control in gardens, orchards and crop fields. Most prey on pests as adults and in their immature, caterpillar-like larval stages. There are about 500 species, or different kinds, of lady beetles in America north of Mexico, and about 65 species in South Dakota. The vast majority are native.
The Asian lady beetles have been getting the most attention lately. That's because of unappealing behaviors that offset their benefits of preying on crop pests such as soybean aphids and European corn borer larvae. Chief among their negative behaviors is a knack for invading houses and other buildings to overwinter. They are most problematic in the fall when large numbers enter homes, and in late spring when they leave. Once inside, Asian lady beetles stain curtains and light colored fabrics and surfaces, and give off an unpleasant odor when handled. Many may die in windowsills, doorways, and poorly insulated rooms and attics, leaving a mess for residents to clean up. The beetles sometimes bite, although their bites are more like a mild pinch and not serious.
Asian lady beetles are also a pest of ripened fruit in the fall--able to break the soft rind of fruits like grapes and peaches or find their way into cracks in the rinds of apples and pears. The beetles become stowaways when fruit is brought inside to make juices, jams and jellies. Keeping Asian lady beetles out of homes requires that windows be effectively screened and that other points of entry are also screened or sealed. Bunches of fall-ripened fruit from gardens and home orchards should be checked and any beetles removed. Several insecticides are also registered for application to the exteriors of buildings to prevent entry of Asian lady beetles. Asian lady beetles found congregating in homes may be vacuumed and discarded.
An Asian lady beetle was discovered in South Dakota in autumn 1996 near Brookings. After a two-year gap, many more Asian lady beetles were found in 1999 in and around Brookings. Since then, the number of beetles has steadily increased, and they have spread across the state. The Asian lady beetle was found near Highmore in central South Dakota by summer 2002, and out west near Nisland by February 2004. The Asian lady beetles in South Dakota came from a population that spread out from an initial point of detection in North America near the port of New Orleans in the late 1980s. A second accidental introduction on the West Coast about the same time likely explains a disjoint distribution of Asian lady beetles west of the Rocky Mountains. Asian lady beetles have been imported into North America on several occasions since 1916 for biological control of various tree pests. Intentional releases of Asian lady beetle were made in several states including California, Washington, Massachusetts, Georgia and the province of Nova Scotia, Canada, but never in South Dakota or other states in the northern Great Plains. All releases apparently failed to establish Asian lady beetle in North America. Since arriving in South Dakota, Asian lady beetles have emerged as one of the most abundant insect predators in soybean fields infested by soybean aphid. Despite their abundance in these fields, lady beetles and other natural enemies have only provided partial--and often inadequate--biological control of the aphids, forcing many growers to spray soybean fields to prevent yield loss from the aphids.
Some would like to see less spraying for the aphid on the million or so acres of soybeans in South Dakota annually. The development of aphid-resistant soybean lines that limit infestation levels may be the answer. In the future, planting lines that limit populations of soybean aphid might also help to reduce the seemingly overabundance of Asian lady beetles. However, Asian lady beetles are not limited to soybean fields, and may flourish in other habitats as well. Research has shown that these beetles have a high degree of invasiveness--the ability to infiltrate and impact various habitats. Asian lady beetles have been found foraging and reproducing in crop fields, roadside vegetation, ornamental shrubs, shelterbelts, natural areas and state parks in South Dakota. They have been found to feed on various kinds of innocuous, non-target aphids and other insects in those habitats.
The Asian lady beetle was preceded in South Dakota by another exotic lady beetle. In 1988, the European seven-spotted lady beetle was found in crop fields near Brookings. There was less ado about the seven-spotted lady beetles, primarily because they, unlike Asian lady beetles, overwinter in leaf litter and not buildings.
It's not apparent that seven-spotted lady beetles have improved biological pest control in the state, but they seem to have impacted other lady beetles. Within a few years of its discovery in South Dakota, researchers had associated the seven-spotted lady beetle with the decline of two to three kinds of native lady beetles--the two-spotted, transverse, and nine-spotted lady beetles. Populations of those native lady beetles have not rebounded. Some fear that the arrival of Asian lady beetle may have similar consequences for native lady beetles, but it could be several more years before that is known. The situation with Asian lady beetles in North America may be analogous to the Greek myth about Pandora's Box, in which misfortunes were released irretrievably into the world. But Pandora also released the character Hope to counter the misfortunes. Similarly, there's hope that ways can be found to capitalize on the benefits of Asian lady beetles as valuable insect predators while identifying ways to minimize their negative aspects.