The G13 strain ofSteinernema carpocapsae(Weiser), previously selected for enhanced host-finding of waxmoth larvae,Galleria mellonellaL., was subjected to selection for the same trait against scarab larvae. Twenty rounds of selection produced a 3.7-fold increase, from 18.4 to 68.7%, in nematode (S20 strain) location of nondiapausing larvae of the Japanese beetle,Popillia japonicaNewman. However, the overall improvement over wild-types (Foundation and All strains), after 33 rounds (13 againstG. mellonellaand 20 against scarabs) was 153- and 72-fold, respectively. Infective juveniles had difficulty locating diapausingP. japonicalarvae, and selection did not result in any enhancement in finding these larvae. Selection for host-finding of scarabs resulted in a 24.6% gain in host-finding ofG. mellonella, suggesting selection was for a general feature present at different levels in different hosts. The use of KOH to absorb CO2resulted in the complete inhibition of S20 strain response to insect hosts, verifying that nematodes have been selected for enhanced sensitivity to CO2. S20 nematodes were significantly less storage stable than the Foundation strain.