Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
The western conifer seed bug (Leptoglossus occidentalis) was first described in the western United States. This true bug of the family Coreidae feeds mainly on the seeds and developing cones of several species of conifers and their respective hybrids. This bug has been expanding its range eastward and was first detected in Pennsylvania in July 1992. Today, its range extends across the northern United States into Canada. Recent records from Pennsylvania and several other areas of the northeastern United States suggest that interstate commerce has been a factor in extending the insect's range.
The western conifer seed bug, which has been seen indoors in western North America, bothers people in homes, offices, and laboratories. In Pennsylvania and other parts of the northeastern United States, this leaf-footed bug becomes a nuisance when it enters homes in search of overwintering sites.
Adults are 3/4 inch long and brownish on top. The upper (dorsal) side of the abdomen is yellow or light orange with five transverse black patches. This orange and black pattern on the abdominal dorsum is revealed during flight. The flight pattern and loud buzz produced by this strong flying conifer pest resemble those of a bumble bee.
Western Conifer Seed Bug Adult
The young nymphs of L. occidentalis are orange, and they become reddish brown after a few molts. The eggs, which are laid in chains on conifer needles, measure about 2 mm each in length.
Western Conifer Seed Bug Nymph
Several morphological characteristics allow L. occidentalis to be distinguished from another native species, L. corculus , which has a similar appearance. First, L. corculus (the leaf-footed pine bug) has a predominantly black abdominal dorsum. Second, while the hind legs of both L. occidentalis and L. corculus have a leaf-like tibial dilation or expansion, the inner and outer dilation of the hind tibia are equal in length in L. occidentalis (Fig. 1a), whereas in L. corculus (Fig. 1b) the outer dilation is distinctly longer than the inner one.
According to observations made in the western United States, the western conifer seed bug produces a single generation each season. Adults emerge from overwintering sites in late May or early June and feed on one-year cones and inflorescences. Eggs laid on host conifers hatch in 10 days, and first instars feed on the needles and tender tissue of cone scales. Later, nymphs use their piercing-sucking mouthparts to feed on developing seeds. Nymphs in all five stages of development and new adults can be observed feeding on the same group of cones by mid-August, at which time the nymphs begin to reach adulthood. Adults feed on ripening seeds until early fall and then seek overwintering sites under pine bark, in dead and dry Douglas firs, and in hawk and rodent nests. At the onset of cold weather, adult western conifer seed bugs may also enter buildings in search of protected overwintering sites.
The western conifer seed bug's consumption of Douglas-fir seeds and seeds of various other species of pine results in a substantial loss of seed crop. Thus, its direct economic impact is a reduction in the quality and viability of conifer seed crops.
Even though this insect does not bite or sting, it causes concern among occupants of homes, offices, and laboratories when it comes indoors. Complaints from residents increase as the insect becomes more active and conspicuous on days in the fall and spring when the temperature is above freezing. In several areas in the northeastern United States, this insect has created great alarm when large numbers of adults suddenly invade houses looking for overwintering sites.
The western conifer seed bug frequently congregates on the outside of buildings in late summer and early fall in the northeastern United States (particularly in New York and Pennsylvania). The large numbers of this insect observed around windows and doors of houses suggests that these are important points of entry.
Where the western conifer seed bug is a persistent nuisance in homes, the best method of control seems to be mechanical exclusion. The following strategies should be followed to prevent this insect's invasion: replace loosely fitting screens, windows, and doors; caulk gaps around door frames, window frames, and soffits; caulk cracks behind chimneys and underneath the wood fascia; screen fireplace chimneys and attic and wall vents.
Authored by: Steve Jacobs, Sr. Extension Associate
February 2002 Reviewed January 2013