Efficacy of two entomopathogenic nematode species as potential biocontrol agents against the rosaceae longhorned beetle, Osphranteria coerulescens, under laboratory conditions

Rosaceae longhorned beetle, Osphranteria coerulescens, is an important pest of fruit trees that attacks all fruit trees belonging to the family Rosaceae in cold regions of Iran. The potential efficacy of two species of entomopathogenic nematodes (EPN), Heterorhabditis bacteriophora and Steinernema carpocapsae, against last instar larvae of this pest was tested under laboratory conditions. In plate assays, the larvae were susceptible to both EPN species but were more susceptible to S. carpocapsae (65.0-97.5% mortality) than H. bacteriophora (42.5-87.8%). Both nematode species were able to penetrate and reproduce within O. coerulescens larvae, but reproduction rate for H. bacteriophora was higher than those of S. carpocapsae; however, the penetration rate for S. carpocapsae was greater than H. bacteriophora. In a migration test on agar plate, S. carpocapsae showed negligible attraction to the pest or to Galleria mellonella cues. However, H. bacteriophora was strongly attracted to the sector of Petri dishes containing larvae. In a test using apricot tree branches, both species of EPN passed from mass frass of O. coerulescens larvae in the tip of the branches, penetrated into the larval galleries, and located and killed the larvae of O. coerulescens in their natural habitat deep inside the branches. Our findings provide the first insight into the biocontrol efficacy of EPN against O. coerulescens larvae, and highlight their potential for the control of this pest. Field experiments are needed to evaluate their potential under the environmental conditions in which rosaceae longhorned beetle larvae are found.