2.2.5. Entomopathogenic Nematodes

Several species of entomopathogenic nematodes were proven to be very effective against the CPB [87,88]. For a laboratory experiment, the effects of native isolates of entomopathogenic nematodes, *Heterorhabditis bacteriophora* Poinar, *Steinernema carpocapsae* Weiser, and *Steinerma feltiae* Filipjev, against late larval stages of CPBs were evaluated at different temperatures. All nematode species achieved higher mortality rates than the control, including elevated success rates under increasing temperatures [89]. In an additional laboratory experiment by Toba et al., fourth instar CPBs were placed in cups containing soil treated with a Mexican strain of *S. feltiae*, and in another with *S. glaseri* Steiner [88]. They found that both nematode species were equally effective against CPB larvae, although different soil and nematode densities could influence the effect. The most common damaging effects against CPB larvae were wing deformation and detained development, which both can affect CPB fitness of adult individuals [90]. Furthermore, Trdan et al. also detected a higher mortality rate of CPB larvae and adults with rising nematode concentrations and temperatures during laboratory bioassays for *H. bacteriophora*, *H. megidis* Poinar, *S. carpocapsae*, and *S. feltiae* [91].

Introduced nematode species from areas elsewhere could be sometimes a more e ffective alternative solution for some areas than naturally occurring nematodes. Their introduction could be necessary as CPB populations may be able to develop tolerances to naturally occurring species as the CPB is also increasingly able to develop tolerances against commercial insecticides [92]. In laboratory experiments, exotic *Heterorhabditis* species, *H. marelatus* Lui & Berry, *H. bacteriophora*, and *H. indica* Poinar, Karunakar & David, were more pathogenic for the CPB than the endemic *Heterorhabditis* strains from Oregon, while the other exotic *Steinernema oregonense* Liu & Berry and *S. riobrave* Cabanillas, Poinar & Raulston species were in the middle of both in terms of e fficacy [92]. Nevertheless, most experiments were only conducted in laboratories. The successful use in the field still has to be proven and would depend on cheap mass production of nematodes as host infection would have to be most likely applied through spraying machines.
