There are several native seed bugs in the PNW. Examples include the boxelder bug (Heteroptera: Rhopolidae; Boisia trivittata), the western conifer seed bug (Heteroptera: Coreidae; Leptoglosus occidentalis), some stink bugs (Heteroptera: Pentatomidae) and many others. Between 2001 to 2005, three new seed bugs in the family Rhyparochromidae, or the dirt-colored seed bugs, have been found for the first time in the PNW. The three new bugs are the tuxedo bug (Raglius alboacuminatus), the bright-spotted ground bug or common smoke bug (Rhyparochromus vulgaris), and the Mediterranean seed bug (Xanthochilus saturnius). Little is known about these bugs, possibly because they are not major economic pests. They do cause anxiety among homeowners and often result in costly eradication. Exotic seed bugs are frequently intercepted at port, primarily on pallets of tile and other ceramic products. Italy represents the origin of many of these interceptions.
Pest description and damage To a gardener, these three seed bugs would look rather similar. They are very small (between 0.25 to 0.3 inch long) and flat and are rapid runners. They all have gray heads with bulging compound eyes. When present in the home landscape, they tend to become very abundant.
The tuxedo bug (R. alboacuminatus) was reported from Utah in 1999. This bug species has two to three white spots, two light bands around the thorax that are visible when viewed from the side or below, banded legs, and a dark abdomen.
The bright-spotted ground bug (R. vulgaris) is found in California and Oregon. It is like a tuxedo bug but has no white rings around the thorax. The legs are uniform in color and the abdomen is light colored.
The Mediterranean seed bug (X. saturnius) is larger than the previous seed bugs with even more distinctive markings of black-on-tan. Behind the head is the thorax with a jet black band followed by a band of stippled brown. The large triangle between the wings (scutellum) is also jet black. A light stripe outlines the scutellum, and the posterior edge of the leathery portion of the wing, forming a distinct X. There are also three other jet black blotch markings on the wings. It can be very abundant in grass seed fields in southern Oregon, indicating that it does feed on grass seed. For that reason, it continues to be regulated in foreign trade. Even though they do not cause damage to houses or harm humans or pets, these seed bugs become a huge annoyance and costly to exterminate when they migrate into households.
Biology and life cycle All the seed bugs overwinter as adults in gregarious clusters in protected places such as under bark or tucked in firewood, or walls of buildings. The adults emerge in spring (April or May) as the weather warms, mate, and lay eggs. Small nymphs look like adults without wings. Adults and larvae feed together on the same plant or on seeds that have fallen to the ground.
The seed bugs are found among tall grasses and weeds, fallow fields, and edges of woodlands, especially those areas with bare ground, where they feed on fallen seeds. Hosts listed include Stachys and other Lamiaceae, and Scrophulariaceae (Verbascum lychnitis). They also feed on seeds of landscape plants such as elm and poplar, as well as nettle, sage, and raspberry. Eggs are laid in the ground litter, on the soil, or on leafy or woody litter. These bugs are seen running about on the ground, litter, or woody debris; there are few direct observations of them feeding on the plants. It is likely they simply feed on grass and weed seeds lying on the ground. The nymphs become mature adults by July and the new adults begin a second generation. These insects become a major nuisance when they move to irrigated grasses from dry pastures. They are an even greater nuisance when they migrate into houses in prodigious numbers. Their impact on seed production, and survival for plants and grasses is unknown. As regulated insects, they can have economic impacts on trade. They create a nuisance, anxiety, and expense for homeowners. Their impact on fragile ecosystems is unknown.
Pest monitoring Their abundance in landscapes generates calls to nurseries and Extension offices when they are encountered by gardeners or the landscape maintenance crews, or when they become more visible on the foundation and siding of houses as they move into homes for the winter.
Management—cultural control
Management strategies are not needed. If the bugs become objectionable, reduce the amount of bare ground (adding groundcovers) among plantings and pull weeds before they set seed. In houses, seal up all cracks and crevices where they might enter and place screens over windows and doors. A vacuum or shop vacuum is very effective in removing bugs.
Management—biological control
There is no mention of natural enemies in their country of origin or here in the PNW. Likely small insectivores like salamanders, frogs, lizards and some birds are potential predators. However, these generalist predators are lacking in urban environments. Given the reports of large numbers of seed bugs entering buildings, predators, that are present, do not consume enough prey.
Management—chemical control
See “True Bugs” in Table 1:
Chemical Control of Landscape Pests
For further information:
LaGasa, Eric. 2006. New Pest Alert and Update; Introduced Exotic Seed-Bugs are New and Increasing Nuisance Problems in Areas of Western Washington - Rhyparochromis vulgaris and Raglius alboacuminatus. https://cms.agr.wa.gov/WSDAKentico/Imported/158-RhyparochromisAndRagliusAlertAndUpdate06.pdf?/158-RhyparochromisAndRagli...
Mediterranean seed bug. http://nathistoc.bio.uci.edu/hemipt/Xanthochilus.htm