Biocontrol Potential of Entomopathogenic Nematodes Against Winter Moths (Operophtera brumata and O. fagata) (Lepidoptera: Geometridae) Infesting Urban Trees

Infectivity and biocontrol potential of entomopathogenic nematodes against winter moths (Operophtera brumata and O. fagata)pupating in the soil were examined in laboratory, semi-field and field conditions. A pilot experiment conducted in the field showed that Steinernema feltiae was completely ineffective against pupae of these moths in the soil. Subsequent laboratory tests revealed that none of the tested species (i.e. S. feltiae, S. affinae, S. carpocapsae, Heterorhabditis megidis and H. bacteriophora) could colonise the pupae, while mature larvae descending to the soil for pupation and prepupae were highly susceptible to nematode infection. No differences were observed between O. brumata and O. fagata in susceptibility to nematodes. In laboratory experiments H. megidis applied at 1.5×10⁵infective juveniles (IJ) m^-2infected almost 100% of insects exposed for 6 days in the soil. It was significantly more infective than H. bacteriophora (73-77%) and Steinernema species (29-50%). H. megidis was also highly effective in semi-field conditions when applied at an even lower dose, i.e. 10⁵IJ m^-2. After a 45-day experiment, only 3% of insects descending for pupation survived in the soil pre-treated with this species. This was significantly less than in soil with S. feltiae (43%) and control treated with water only (59%). Very high efficacy of H. megidis and a relatively easy method for its field application through ground spraying gives some promise for environmentally safe and successful biological control of winter moths during their pupation in the soil. The low application rate required and recycling in the host could be additional advantages for economic and long lasting protection of high value trees, particularly those in urban parks and forests.