Asian Invasion

September 21, 2010 1 Comment

Ahhh.  Fall… when the tomato plants turn brown but still try to put out a couple of fruits, the heat and humidity drop (usually!), and the Asian Lady Beetles return to our consciousness.

Asian lady beetles are 1/3 inch in length, dome-shaped, are yellowish-orange to red with variable black spots on the back (19 of them). Deep orange is the most common color. The spots may be faint or missing and there is a black "W" shaped mark on the thorax (right behind the head).

What we know as the Asian Beetle is the multicolored Asian lady beetle or Harmonia axyridis.  It isn’t clear where the Asian lady beetle originated, but they arrived by accident in ports like New Orleans in the late 1980s and have been crawling and flying themselves to all corners of the country. 

Asian lady beetles are beneficial insects by eating other pests in trees during the summer and in fields and gardens during the fall.  They eat aphids and that is worth keeping them around for me.  However, our problem with them is during the cold season when they enter our houses. 

In their natural habitat, Asian lady beetles overwinter in large congregations in the cracks and crevices on cliff faces.  Since we don’t have a large number of cliffs in the Iowa, the side of a house looks just as good to the beetle.  They fly to sunny, exposed surfaces as they get ready to hibernate through the winter. They will crawl around and find any sort of crevice and often end up crawling into our homes.  This makes them accidental invaders.  They do not feed or reproduce indoors and they cannot attack the house structure, furniture or fabrics.  They don’t sting or carry diseases, but they can pinch, may leave a slimy smear and they have an odor when squished.  They are just downright annoying.

Asian lady beetles enjoy eating aphids and Soybean aphids are a pose of the, wouldn’t you know it, soybean.  I know everyone thinks that now that the beans are being harvested they will be flocking to your home.  And some of them may, but the timing of the beetle flight varies.  It is usually from mid-September through October, but depends mainly on the day length and the weather.  The first warm day after the first fall frost will find those beetles trying to find their winter spots.  So far, it looks like the frost is a little ways away this year.

So how do you keep them out of your house.  Well, you need to seal exterior gaps and cracks around windows, doors, eaves, roofs, siding and other points of access before the beetles appear.  Sounds simple, right?  Probably not since it is time consuming, impractical and usually not 100% effective.  For large infestations you can try spraying pyrethroid insecticides such as permethrin or esfenvalerate to the outside of buildings when the beetles appear to help prevent them from getting in.  Indoor insecticides usually don’t work well because it is impossible to reach all of the lady beetles that are hidden in the walls.  The best thing to do is vacuum or sweep them up and discard if they are already in the house.  And for long-term relief, plant trees that will grow to shade the south and west sides of the house.   That way you don’t have to drag the vacuum out each time you see one!

Dig it!

Filed in: Autumn, Pests

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  1. KLD says:

    I have found a product called BugSlayer that is sold at places like Menards. This stuff really works. Last year I didn’t find any of the Beetles in the house, but there was a ring around the foundation of the house of dead beetles where I had sprayed the product. It is on the pricey side, but well worth the money as it protects against other pests as well!

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