Evaluation of above-ground application of entomopathogenic nematodes for the control of diapausing codling moth (Cydia pomonella L.) under natural conditions

摘要

In South Africa, after harvest and prior to the winter months, when the entire codling moth population enters diapause, no control measures are applied in apple and pear orchards. The biocontrol potential of three imported entomopathogenic nematode (EPN) isolates, being Steinernema feltiae and two isolates of Heterorhabditis bacteriophora (Hb1, Hb2), as well as a local isolate, S. yirgalemense, were evaluated for the control of codling moth under local conditions. All concentrations of S. yirgalemense, applied by immersion in a suspension of nematodes, gave >98 % control. The in vivo-produced S. yirgalemense resulted in codling moth control of >90 %, compared to 54 % and 31 % control by the H. bacteriophora Hb1 and Hb2 isolates, respectively. In follow-up field trials, S. feltiae resulted in % control, and was more effective than both the S. yirgalemense and the H. bacteriophora (Hb1) isolates. To validate the data obtained from the field trials, subsequent laboratory bioassays were conducted evaluating temperature regimes, following the same cycle as under natural conditions, with a constant humidity of 100 %. Steinernema feltiae proved to be most effective, causing >90 % mortality, followed by S. yirgalemense, with 78 % mortality. The two H. bacteriophora isolates (Hb1, Hb2) under the above-mentioned laboratory conditions, resulted in 73 % and 59 % control, respectively. Humidity, thus, seems to be the most important factor affecting EPN efficacy during above-ground applications. From the results obtained, it can be concluded that H. bacteriophora will not be suitable for the control of codling moth, with S. feltiae proving to be a better candidate than S. yirgalemense for such control purposes.