During the cooling-off season, between the late summer and throughout the fall, the change from warm to cold weather triggers some insect species to look for warm overwintering sites.

Usually, foreign grain beetles are the first insects to be noticed indoors, followed in order by cluster flies, paper wasps, boxelder bugs, multicolored Asian lady beetles and western conifer seed bugs. The order of fall invasion of course varies depending on the species, temperature and geographical distribution of insects.

The selection criteria of overwintering sites are not fully understood, but it is quite possible that the shape, color or location of the structure could be reasons that attract certain pests to a particular site. Once indoors, fall-invading insects are not only annoying, but they also can stain light surfaces when crushed, can trigger asthma attacks due to odors of their carcasses, and can attract hide beetles, larder beetles, carpet beetles, carpenter ants, and other insects that love to feed on them. Therefore, management of fall-invading insects is a necessary task for our businesses.

EXTERIOR TREATMENTS. The only feasible management method for these pests is keeping adults out and destroying those that enter the structure. To do so, exterior applications of a proven, long-lasting residual insecticide should be employed during the early fall. These applications should target the sunny sides of the building (south and west), where fall-invading insects congregate before they finally conceal themselves in protected places.

In addition, thoroughly treat under eaves, overhangs, under siding, around windows, around doors, and around vents and all possible entry sites of exterior walls (following the pesticide’s label directions). However, an extended summer or heavy rains may render an initial treatment ineffective; accordingly, another treatment may be needed/justified in late September or early October to maintain protection.

INTERIOR TREATMENTS. Usually, indoor treatments for fall-invading insects are not required unless they already have entered the structure, especially in big numbers. In this situation, if not properly treated, these bugs will be a nuisance and will persistently show up in living places throughout the winter.

Dealing with overwintering insects indoors can be challenging for pest management professionals. This is due to a number of reasons. For example, the insects at this time are not very mobile, which limits their exposures to pesticides. Also, they are concealed in deep voids, making them inaccessible to treatments. Finally, they could be in any number of hiding places, rendering the pesticide applications unfeasible.

However, if applications of insecticides are needed, carefully use an approved residual insecticide to apply crack, crevice, void and spot treatments to all hiding and congregating areas. Treat attics, crawlspaces, empty roof spaces, vent openings and ceilings. It is recommended to remove outlet plates and lightly apply residual insecticidal dust to the voids behind them. Insect light traps (ILTs) can be used to reduce the numbers of flying insects in sensitive places.

To help your customers prevent fall-invading insects, in the summer and before late fall/early winter, recommend they properly seal or caulk cracks, crevices, voids and all possible entry openings in and around the building. Also, remind them to screen windows, doors, ventilators and louvers.

The author is technical and training director at Adam’s Pest Control, Medina, Minn.

Bates, S.L. 2005. Damage to common plumbing materials caused by overwintering Leptoglossus occidentalis (Hemiptera: Coreidae), Can. Entomol.137: 492-496.