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 vegetation sampled. Three insects of significance as predators of pests in Australian lucerne were studied: transverse ladybird beetle (Coccinella transversalis Fabricius), pollen beetle (Dicranolaius bellulus (Guérin-Méneville)), and spined predatory shield bug (Oechalia schellembergii (Guérin-Méneville)). In a preliminary experiment comparing a commercially harvested area of lucerne with an unharvested area within the same crop, the proportions of released insects recaptured from unharvested lucerne were significantly lower than recoveries from the shorter, harvested lucerne. Resampling the tall lucerne after it was cut by hand gave cumulative recapture proportions which did not differ from those observed for the harvested lucerne. A second experiment with a randomised replicated design re-tested the hypotheses of the preliminary experiment for two insect species. Very similar results were obtained. This verification showed that recapture efficiencies from tall lucerne ranged between 0.60 and 0.74 but that resampling after hand cutting gave cumulative recapture proportions in excess of 0.86 which did not differ from recapture proportions from short lucerne.