According to the Idaho State Department of Agriculture, the elm seed bug, Arocatus melanocephalus, of the Hemiptera order and Lygaeidae family, was first detected in the United States in 2012 in two counties in Idaho. It then traveled down through Utah and started being seen in significant numbers in Grand County in 2015. The positive aspect of this insect is it primarily feeds on the seeds of elm trees, which our Siberian elms generously share with us. The negative aspect is that while it doesn’t pose a threat to people or buildings, it’s proven to be an incredible nuisance due to its desire to be indoors.
Elm seed bugs overwinter as adults in leaf duff, woodpiles, and other places they can hide and in the spring mate and lay eggs on elm trees. The larvae feed on the elm seeds and due to the number of elms in the area, we have many seeds and so lots of elm seed bugs.
Elm seed bugs are one-quarter to one-third-inch long, dark in color, with a reddish-colored abdomen on the underside and as with many Hemiptera, their crossed wings create an “X” pattern on their backs. There’s also a triangular black shield-like plate on their backs, called the scutellum, which is sided with a reddish color.
As mentioned, the biggest issue with this insect is that it likes to come inside buildings. As with all inside-loving insects, control measures start by making your house as tight as possible, and I mean tight, since this insect is small. So you need to cover, caulk or otherwise fill up any outside cracks, install weather stripping around doors and windows, put screens over vents and repair window screens and make sure they fit tight. Beyond that, I suggest you buy a really good hand vacuum to vacuum them up, but don’t just dump them outside since many will just find their way back in but rather dump them in a bucket of soapy water.
Other control options include putting sticky traps around your windowsills since once they are inside they like to hang out on the windows. Something that would help early in the season would be raking up and getting rid of any elm seeds around your property. This suggests to some that perhaps the best thing would be to cut down the elm trees but that is hard to do if they are giving you shade.
If you are thinking of using insecticides you might ask, are there any that will control them. The answer is yes and no. Yes, you can spray a broad-spectrum insecticide around the outside of the house Spray outside around closed windows and doors, vents, etc., and three feet up the side of the building. Formulations with bifenthrin, carbaryl, deltamethrin, lambda-cyhalothrin, malathion, and permethrin could work – but only for a while – from one week to maybe a few weeks. Please pay attention to the pesticide label; more isn’t better and is in fact illegal. You must follow the label directions. The “no” answer comes because the spray is not going to give you complete control, meaning it isn’t going to stop them all. It’s also not suggested you spray inside the home but rather vacuum, vacuum and vacuum.
Unfortunately, it is likely this pest is here to stay, but luckily the numbers seem to wax and wane over the season. So good luck if you are having to deal with this insect pest!
Previous articles can be found on The Times-Independent website. If you have a topic you would like to know more about, call the Utah State University Extension Grand County office at 259-7558 or email Mike at firstname.lastname@example.org.