A Pitfall Trapping Survey of Darkling Beetles in Desert Steppe Vegetation

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Abstract
A pitfall trapping survey of autumn emergent darkling beetles was conducted on the Hanford Reservation, Benton County, Washington, in 1963. Forty—nine pitfall traps were arranged in a grid pattern in greasewood and sagebrush communities. Quantitatively, the beetle catch was composed almost entirely of two species Pelecyphorus densicollis and Stenomorpha puncticollis. These appeared in the traps in September and reached a peak of abundance in mid—October. Trap catches declined until early December when the beetles were killed by the onset of cold weather. A total of 4,378 beetles was captured, marked, and released. An estimate of beetle population indicated that about one thousand more beetles were present in the sagebrush community. Stenomorpha was more abundant than Pelecyphorus in either community, but more Pelecyphorus occurred in sagebrush than in greasewood. A dense sward of cheatgrass in the greasewood community appeared to reduce the catch of Pelecyphorus but not Stenomorpha. Pelecyphorus showed a predilection for open ground between shrub canopies but Stenomorpha predominated on ground beneath the shrub canopies. On the average, Stenomorpha weighed more than Pelecyphorus. This resulted in a beetle biomass of approximately the same magnitude in both communities.