The aim of the study was to determine the potential of three Bulgarian isolates of еntomopathogenic nematodes, Heterorhabditis bacteriophora, Steinernema arenarium and S. feltiae, respectively, for the biological control of the codling moth Cydia pomonella, a common economically important pest in apple orchards. A laboratory trial was set up to evaluate the susceptibility of fifth instar larvae of the insect to equal concentrations of infective juveniles of the three nematode isolates over a 72-hour period and the mortality was recorded at three-hour intervals.
The overall statistical analysis of the obtained data showed that the nematode species factor had a significant effect on the parameters of life duration and mortality rate, and the survival curves of C. pomonella larvae after exposure to infective juveniles. S. feltie was most effective in controlling the codling moth with lowest average life duration of the larvae after exposure and 100% mortality as early as the 42nd hour of the experiment.
The Kaplan-Meier Survival Analysis and the subsequent all pairwise multiple comparison procedures following the method of Holm-Sidak showed significant differences between the survival curve of larvae parasitized with S. feltiae and the curves for the other two variants. Nevertheless, H. bacteriophora and S. arenarium also performed well with 97% and 83% larval mortality, respectively, for the full duration of the trial. The results demonstrate the suitability of Bulgarian isolates of entomopathogenic nematodes for biological control of C. pomonella.