September 24, 2004
Asian lady beetles set to return, but their numbers are lower
WEST LAFAYETTE, Ind. – Homeowners weary of their annual fight with Asian lady beetles may see fewer this year.
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Tim Gibb, a Purdue Extension entomologist said Asian lady beetles will still be around, but there are indications that their numbers could be down when compared to last year.
"From sampling in soybean fields, the early indications are that the population of lady beetles will not be as high this year as it has been the past couple of years," Gibb said. "Using that as an indicator of whether or not we're going to have beetle pressure in homes, it may be telling us we're not going to have as big a problem."
The decrease is probably due to lower soybean aphid numbers throughout the state. The lady beetle is a natural predator of aphids.
"Part of the reason that the Asian lady beetle population has been fluctuating over the last few years has to do with food sources," Gibb said.
Scientists think soybean aphid numbers where low this year for a couple of reasons.
Larry Bledsoe, an Extension entomologist, said most soybean aphids ride to Indiana on wind currents and storm fronts from the upper Mississippi valley. Spring rains in that area this year discouraged aphid activity.
"Spring rains there delayed planting so that the timing was not right for the aphids to colonize young soybean plants," Bledsoe said. "Also persistent storms after planting interfered with widespread colonization of the aphid. Lastly, Asian lady beetle numbers were unusually high last fall, which probably meant fewer aphid eggs overwintered relative to the previous year."
Although their predatory instincts are beneficial to farmers, the beetles have garnered a bad reputation with homeowners.
"Beginning in the latter part of October, the Asian lady beetle has a peculiar behavior of wanting to congregate in large groups inside buildings," Gibb said. "This becomes particularly troublesome if the building they've chosen happens to be your home."
Entomologists believe the beetles are attracted to buildings because – to the beetles anyway – the buildings look like cliffs in their native Asia.
"Their native habitat included high cliffs," Gibb said. "After feeding during the summertime, the beetles would head toward these tall outcroppings or cliffs and get into the cracks and caves to pass the winter.
"In Indiana we don't have many cliffs, but we do have tall, two-story homes that are light colored with windows or shadows that look like cracks or caves to the beetles."
Even if overall beetle numbers are down, that doesn't mean homeowners won't have problems.
"The key to controlling Asian lady beetles is to keep them out of the house in the first place," Gibb said. "Putting a preventative insecticide on the outside of the home in the middle of October will do wonders in keeping these things from appearing inside the home later."
Gibb suggests putting an insecticide containing a synthetic pyrethroid around windows, doors and under eaves, particularly on the south and west sides of the home. Other places where there is light and dark contrast also are attractive to the insects.
"Often the beetles will tell you where to treat if you just watch them and see where they begin congregating," he said.
It's better to stop the beetles before they get inside, because once in the walls they are protected.
"A nice warm day in the middle of winter will reactivate the beetles, and they begin searching for a way back out of the wall void. In so doing, they often end up inside the home."
If left untreated, beetles can congregate by the thousands inside homes. If they do get inside, Gibb's best advice is to vacuum them up.
"After October it becomes difficult to control them, because the majority are still inside the wall voids where we can't get insecticides to them," he said. "They don't all reactivate at once. Even if indoor labeled insecticides are used in the home, the beetles inside the walls are going to continue to slowly appear. It will require daily vacuuming to stay ahead of the beetles reemergence."
Control recommendations for Asian lady beetles are available from Purdue Extension through a local Extension educator, the toll-free hotline (888) EXT-INFO, and on the Web.
Writer: Kay Hagen, (765) 494-6682, kjh@purdue.edu
Sources: Tim Gibb, (765) 494-4570, gibb@purdue.edu
Larry Bledsoe, (765) 494-8324, lbledsoe@purdue.edu
Ag Communications: (765) 494-2722; Beth Forbes, forbes@purdue.edu
Agriculture News Page
PHOTO CAPTION:
Asian lady beetles, such as this one, appear every October and make their way into homes. This year entomologists think there might be fewer beetles for homeowners to contend with. (Purdue Department of Entomology photo/John Obermeyer)
A publication-quality photo is available at https://www.purdue.edu/uns/images/+2004/gibb-lady.jpg
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