Boxelder Bugs and Their Control
Boxelder bugs, Boisea trivittatus, often become pests when large numbers of them appear in houses or congregate on the sunny sides of buildings in the fall, late winter and early spring. Although there are reports that they bite people, this is apparently very rare. They do not damage buildings, furniture, clothing or food, but can spot curtains and walls with fecal material and produce a foul odor when crushed. Therefore, they are principally a nuisance because of their presence, especially when they crawl or fly about rooms.
Adult boxelder bugs are about inch long, dark brown to black with conspicuous red markings on their backs. They are flat and their wings overlap on their backs. The young or nymphs are wingless but generally similar in shape to the adults. The smaller nymphs are solid bright red, while the older nymphs have some black markings. They molt five times to become adults. Males and females look alike.
Boxelder bugs are especially numerous where seed-bearing or female boxelder trees, Acer negundo, (also known as ash-leaf or three-leaf maple) are found. Not surprisingly, the female boxelder tree is the preferred host of these insects. Although boxelder bugs will occasionally feed on ash, maple, plum, cherry, peach, pear, grape plus other trees, shrubs and grasses, they do not appear to build up to nuisance numbers unless they feed on boxelder trees.
In the fall, swarms of adult boxelder bugs may be seen on the trunks of trees and on the south side of buildings. At this time, the adults begin to migrate into sheltered places to pass the winter. They select such locations as various cracks and crevices, hollow tree trunks, litter and trash piles, barns, other outbuildings and homes. They hide in wall voids, door and window casings, under shingles and shutters, in attics and basements, around foundations and whatever other protected spots they can find. They remain in these locations during the evenings in cool weather but resume activity during sunny, warm days of fall.
Activity ceases during most of the winter, but the bugs may appear for brief periods during sunny, warm days in late winter and early spring, especially on house siding or on windows of rooms with a southern exposure or sometimes in the rooms themselves. They have even been reported on snow.
In the spring when buds appear, the bugs leave their winter quarters and seek host plants on which to lay their eggs. The females lay tiny, rusty-red, oval eggs in bark crevices, on leaves and other parts of female boxelder trees. They will also lay their eggs on other trees as well as on grass, litter, fences, stones and other places.
The young bugs or nymphs hatch in about two weeks and feed by inserting their beaks and sucking the plant juices of leaves, fruits and soft seeds. Their feeding causes little injury to boxelder trees but may result in the dimpling of some tree fruits. They continue to feed through the season and become adults in late summer and early fall. The onset of cool weather signals the start of their migration to winter quarters.
One and sometimes two generations per year are common in Connecticut.
Host Removal: The most satisfactory and permanent method of control, in situations where boxelder bugs are a recurring problem, is the removal of nearby seed-bearing or female boxelder trees. This is not always a practical solution, however, if nearby boxelders are not on your property. In addition, the trees may be located quite far away; it is known that boxelder bugs can migrate for considerable distances.
Outdoor Chemical Control: Boxelder bugs are difficult to control outdoors with insecticides under any circumstances. This is mostly a result of the fact that the effectiveness of most insecticides (except pyrethroids) is directly related to temperature. The warmer it is the more effective they are; the cooler it is, the less effective they are. This increase or decrease in effectiveness pivots at around 70oF. Unfortunately, boxelder bugs tend to be nuisances when temperatures are normally much lower than 70oF. In addition, the insecticide residues do not last for much more than a week.
Spraying Infested Outdoor Premises: As boxelder bugs mature, they leave their host trees and usually mass at the bases of these and other trees, along fence rows, around foundation walls and other places. Insecticides are most effective when applied directly on the bugs, but they can also be relatively effective if enough spray is applied to thoroughly wet all surfaces over which the bugs crawl. Several gallons of spray are generally required. When treating the foundation, spray thoroughly up into the area where the siding overhangs the foundations, into all cracks and crevices along breezeways and patios and around all windows and door frames and hatchways up to about three feet above the ground.
Indoor Preventative Treatment: It is very useful to prevent entry into homes by applying caulking compound around lower window and door frames as well as other cracks and crevices around the foundation and siding within about three feet of the ground.
Spraying Indoors: The use of aerosols registered for indoor insect control may kill the insects that are sprayed, but they do not control the continued migration of additional boxelder bugs. Indoor control with pesticides can be very difficult and is therefore not recommended. The recommended control indoors is to vacuum the insects up and dispose of the contents of the cleaner bag promptly.
Originally written by: Milton G. Savos, Professor Emeritus
Revised by: Edmond L Marrotte, Consumer Horticulturist, Department of Plant Science, University of Connecticut
Updated by: Mary Concklin, IPM, University of Connecticut. 2011
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