Capture of wild and marked Agriotes obscurus in pheromone traps according to distance, wind direction and date of trapping

A study was conducted to determine rates of recapture of marked Agriotes obscurus (AO) males released in a grassy field on four occasions in the centre of pheromone trap squares with traps spaced 2.5, 5.0, 7.5 and 10.0 m apart. Concurrent catches of naturally occurring and naturally dispersed (wild) AO were also recorded. Catch of marked AO was highest during peak emergence when maximum weekly temperatures ranged from 15.7 to 17 °C, and rainfall was light. Mean catch in the 2.5–10.0 m trap squares was, respectively, 82.0, 79.0, 77.0 and 65.0%, which occurred within one week of release. Catch of marked AO were lower (range in 2.5–10.0 m squares: 74.5–50.5%) when released early in the activity period, due to lower temperatures and higher rainfall, and catch was protracted over 3 weeks. Catch during two releases under favourable weather late in the activity period was also reduced (range: 25–58%), likely due to loss of AO vigour and/or pheromone trap efficacy. Catch of wild AO was highest in traps spaced 7.5 or 10.0 m apart, suggesting independence of these traps, and between-trap competition at 2.5 and 5.0 m spacings. From these data, we estimated that an effective spacing for traps in mass trapping arrays would be approximately 6 m. Significantly higher catch of marked or wild AO occurred in traps that were upwind in all trap squares, indicating wind direction should be considered in structuring the placement of trap arrays in mass trapping programs in non-farmed headland areas.