RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS WITHIN THE RIBOSOMAL DNA REPEAT UNIT OF BRITISH ENTOMOPATHOGENIC NEMATODES (RHABDITIDA, STEINERNEMATIDAE)

Genomic DNA extracted from entomopathogenic nematodes isolated from 89 soil samples taken throughout the United Kingdom was hybridized with the ribosomal DNA clone from Caenorhabditis elegans (pCe7). When the DNA was digested with EcoR I and Hind III in a double digest, 5 distinct RFLP (restriction fragment length polymorphism) types were observed. While the prevalence of the 5 types was not equal, no correlation with geographical location, soil type or habitat could be detected. Subsequent hybridizations of total genomic DNA from the various RFLP types divided them into 2 groups. The most prevalent group, identified as Steinernema feltiae ( = bibionis), contained 2 of the RFLP types (A1 and A2). The other group contained the remaining 3 RFLP types (B1, B2 and B3). Although similar to S. feltiae (= bibionis), the members of the B-types can be distinguished from this species on morphological grounds and preliminary crossbreeding experiments have demonstrated that the 2 groups are reproductively isolated.