Distribution of Billbug Species and Their Seasonal Lifecycles in Idaho.

Billbug damage is an increasing problem on southern Idaho golf courses and home lawns.  Three billbug species, bluegrass (Sphenophorus parvulus Gyllenhal), hunting (S. venatus Say) and Rocky Mountain (S. cicatristriatus Fabraeus) have been reported as damaging to turfgrass in the Pacific Northwest.  Except for the bluegrass billbug, the distribution and biology of these species are not completely understood.  Linear pitfall traps were placed in 10 and 12 locations in 2006 and 2007, respectively, throughout southern and central Idaho.  Locations included golf courses, home and business lawns and a highway interchange park.  Traps were monitored weekly for adult billbug activity and cores were taken to evaluate larvae occurrence at some locations.  Weekly soil samples for larvae occurrence were taken using a 10 cm diameter cup cutter.  Monitoring results confirmed the presence of S. parvulus, S. cicatristriatus, and S. venatus species in the Treasure Valley during 2006 and 2007 as well as in Twin Falls in 2007.  In addition to these three species, we confirmed the presence of Phoenician billbug (S. phoeniciensis Chittenden), which had previously not been known to occur on cool-season turf.  S. parvulus comprised up to 91% of the adults collected, while S. cicatristriatus, S. venatus and S. phoeniciensis comprised up to 100%, 46%, and 33%, respectively.  Only two species, S. parvulus and S. cicatristriatus, were collected in eastern Idaho locations in both years. Core sampling at several locations revealed the presence of larvae in April prior to adult activity and continuing late into the season at some locations.  This confirms previous reports on the over-wintering capability of larvae for S. cicatristriatus and possibly S. venatus.  The presence of four billbug species were confirmed in southwest Idaho with only two occurring in eastern Idaho.