Drought changing insect behavior

Photo courtesy www.bugguide.net
Nathan Reade, Inyo-Mono Ag Commissioner, and Dustin Blakey, Inyo-Mono Farm Advisor
County of Inyo

What are these black bugs showing up on houses, fences and even indoors this year?
The western boxelder bug, or Boisea rubrolineata, is a native insect that is rarely noticed during normal climate conditions. The half-inch-long bug is mostly black but does have three thick red lines running down its back, sometimes accompanied by several thinner red lines on its wings.
Boxelder bugs are usually found congregating in large groups on rocks, fences, sidewalks and even the sides of buildings, but rarely venture indoors. This year has been an exception. Warmer winter months and drought conditions seem to have created prime conditions for populations of the boxelder bug to explode.
These bugs can be a nuisance when they enter homes and other buildings, and will continue to do so until temperatures cool. The next generation, which will be adults in late August, is more likely to enter homes and structures. Taking the time to ensure screens are in good condition and caulking or sealing openings into homes will help prevent entry this late summer and fall. Luckily, these bugs are not known to be an agricultural pest. They do not cause significant damage to landscape plantings or gardens. They also do not injure people or pets.
Control of this insect is very difficult, and many insecticides are ineffective on the boxelder bug. The University of California recommends vacuuming the bugs or washing them from walls or tree trunks with a forceful stream of water where larger populations exist. The bugs emit a pheromone that attracts more bugs to the area, which is why they are commonly found in large groups. Washing outside areas with soap and water can help to reduce this attractant. Removing debris such as piles of rocks and leaves eliminates daytime hiding places for these insects as well as overwintering sites. Elimination of host material is a last resort. Boxelder bugs prefer boxelder, maple, ash and liquidambar trees.
For more information, feel free to contact the Inyo-Mono Agricultural Commissioner’s Office at (760) 873-7860.