Flight activity and dispersal of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) across a mixed agricultural landscape in southern Australia

To better understand the field ecology of stored grain beetles in southern Australia we monitored the flight activity of Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) over a 2 year period. We used target-specific pheromone lures and Lindgren funnel traps in open fields, at grain storages, and in remnant native vegetation. Over 35,000 R. dominica and 2,500 T. castaneum were caught. Significantly more R. dominica (46.4%) were caught in areas of remnant vegetation than at storage sites (29.2%) or in open fields (24.4%), suggesting this species may be utilising non-grain food sources in some areas. In contrast, the majority of T. castaneum (45.4%) were caught adjacent to storages. An intense summer heatwave (14 day mean maximum air temperature 41.9 °C) corresponded to captures of both species declining to near zero until the following spring. Sex ratios of both species varied significantly over time but were unaffected by habitat type. Two mark/release/recapture (MRR) trials using laboratory-reared R. dominica were conducted using a 1 km trap array and pheromone lures. The recovery rate for marked beetles in the first trial was 1.41%, however a subsequent experiment comparing fresh and weathered lures showed that lure attractancy declines to 50% between 3 and 4 days after deployment during hot weather (mean daily maximum air temperature 29.4 °C). When the MRR trial was repeated with lures replaced at shorter (2 day) intervals, the recovery rate rose to 3.27% and the number of wild R. dominica captured increased proportionately. The short half-life of rubber septum-based R. dominica pheromone lures needs to be considered when designing surveillance programs, particularly if attempts are being made to correlate R. dominica dispersal patterns to short-term weather events.