GENETIC ADAPTATION AND FOUNDER EFFECT IN LABORATORY POPULATIONS OF THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA-GLASERI

Laboratory culture can have detrimental effects on populations through adverse environmental conditions such as poor nutrition or disease, o r through genetic effects such as inbreeding depression, founder effec t, genetic drift, or laboratory adaptation. We tested for laboratory e ffects on the entomopathogenic nematode Steinernema glaseri (Steiner) by forming a genetically diverse base population from a series of fiel d isolates and rearing several independent lines through 12 cycles of laboratory culture, using larvae of the greater wax moth, Galleria mel lonella (L.), or the Japanese beetle, Popillia japonica Newman, as hos ts. Laboratory bioassays based on G. mellonella indicated that lines m aintained with large breeding populations did not deteriorate but ofte n showed significant increases in infectivity (15.3-48.0%), proportion of males (12.2-36.1%), and reproductive potential (39.0-160.4%). Line s reared on P. japonica larvae responded similarly to lines reared on G. mellonella but showed higher levels of reproductive potential. Two of three lines subjected to initial genetic bottlenecks to test for fo under effects differed from other lines by showing very high infectivi ty but little change in sex ratio or reproductive potential. These res ults demonstrate that laboratory adaptation can produce dramatic chang es in important biological attributes of these nematodes, but that a l ack of genetic variation associated with founder effects can impede th is process. Laboratory adaptation should be considered a potent factor when designing, interpreting, and comparing studies of this important group of biological control organisms.