Fly-free cherries: utopia or realistic hope?

In 2002 until 2004, first experiments to control the European cherry fruit fly Rhagoletis cerasi were carried out under laboratory, semi-field and field conditions with several entomopathogenic nematode species and strains. In the laboratory the efficacy of nematodes against R. cerasi larvae, pupae and adults was examined. Different nematode dosages, exposure temperatures and substrates were tested in cell wells, petri dishes and plastic boxes. In the semi-field experiments plastic fruit boxes, filled with soil, were used. In the field tests R. cerasi-larvae and nematodes were released in defined areas in a cherry orchard and emerging flies recaptured in the following season. For evaluation of the experiments, the infestation rates and efficiencies (Abbott) were determined. Steinernema carpocapsae and S. feltiae achieved the highest efficacies. In laboratory, infestation rates in cell wells up to 91 % and efficencies up to 96 %, in petri dishes up to 96 % respectively 98 % and in plastic boxes 88 % respectively 89 % were attained. The experimental substrates like quartz sand or soil type and the tested temperatures did not result in consistent significant differences in laboratoy tests. A dosage below 25 nematodes per cm² resulted in insufficient infestation rates. In the semi-field experiments a maximum infestation rate of 86 % (efficiency 78 %) and in the 2002/2003 field test an efficiency of 88 % was obtained. In the second field test 2003/2004 the efficacy was 56%. That unsatisfying result might be connected with the high soil temperatures (27°C - >30°C) during nematode application in 2003. While R. cerasi-pupae were not infested, infestation rates up to 40 % were observed for adults when hatching from pupae in nematode-infested sand in the laboratory. These results indicate a high controlling potential of entomopathogenic nematodes against R. cerasi, especially of the steinernematid species S. carpocapsae and S. feltiae. Further experiments under realistic conditions in the field are forcibly necessary before putting this control method into practice. These experiments are planed for 2005 until 2008