Capture efficiency of insect natural enemies from tall and short vegetation using vacuum sampling

Experiments were conducted in lucerne to determine the efficiency of vacuum sampling of insects and whether this was affected by the height of vegetat ion sampled. Three insects of significance as predators of pests in Austral ian lucerne were studied: transverse ladybird beetle (Coccinella transversa lis Fabricius), pollen beetle (Dicranolaius bellulus (Guerin-Meneville)), a nd spined predatory shield bug (Oechalia schellembergii (Guerin-Meneville)) . In a preliminary experiment comparing a commercially harvested area of lu cerne with an unharvested area within the same crop, the proportions of rel eased insects recaptured from unharvested lucerne were significantly lower than recoveries from the shorter, harvested lucerne. Resampling the tall lu cerne after it was cut by hand gave cumulative recapture proportions which did not differ from those observed for the harvested lucerne. A second expe riment with a randomised replicated design re-tested the hypotheses of the preliminary experiment for two insect species. Very similar results were ob tained. This verification showed that recapture efficiencies from tall luce rne ranged between 0.60 and 0.74 but that resampling after hand cutting gav e cumulative recapture proportions in excess of 0.86 which did not differ f rom recapture proportions from short lucerne.