Potential control of cabbage root fly (Delia radicum) with thepredatory staphylinid beetle Atheta coriaria

Abstract: The predatory staphylinid beetle, Atheta coriaria, was investigated as a potentialbiological control agent for cabbage root fly (CRF) (Delia radicum). Initial predation bioassaysconfirmed that A. coriaria adults eat both CRF eggs and young larvae. Subsequent workdemonstrated that it was possible to ‘seed’ plant-raising modules with A. coriaria in thepropagation glasshouse. By adding an artificial food source (turkey-rearing crumbs) to thecompost, A. coriaria was able to colonise and breed in modules during the propagation period.Modules prepared in this way were then used in a semi-field experiment to test whether theA. coriaria that had established in the modules could reduce the severity of CRF damage tocauliflower plants once planted out. CRF eggs were added to the soil around each plant over a 2-week period, to simulate second generation CRF egg laying. Significantly less CRF root damagewas recorded in plants where beetles had been reared in modules during propagation comparedwith untreated control plants. Similarly, plants treated with high numbers of beetles after plantingout had significantly less damage than control plants. The efficacy of A. coriaria used either to‘seed’ modules during propagation or applied to plants after planting out was tested in the field in2009. Results compared A. coriaria-treated plants with modules drenched with chlorpyrifos orspinosad and with untreated control plants. More untreated control plants died as a result of CRFfeeding, and root weights of surviving plants were lower, compared with A. coriaria- orinsecticide-treated plants. The number of plants dying as a result of CRF feeding, and rootweights of surviving plants, were similar in both A. coriaria and insecticide treatments. However,root damage index assessments did not differ significantly between treated and untreated plants.Although further work is required, results so far indicate that A. coriaria, applied to modulesduring propagation or after planting out, has potential for cost-effective biological control ofCRF.