Bacillus thuringiensis as a marker for insect dispersal studies

Laboratory studies confirmed that commercial formulations of Bacillus thuringiensis (Bt) could be used to mark potato tuber moths, Phthorimaea operculella. Moths were successfully marked by direct application or through indirect acquisition by contact with marked surfaces such as a leaf or a Petri dish. Marked moths were identified by the distinctive crystalline morphology of different subspecies of Bt, allowing the separation of individual moths marked with either Btk (kurstaki) or Bti (israelensis). A simple microbiological method for processing the trapped moths before definitive, microscopic identification of the subspecies is described. Field marking was verified by capturing light brown apple moths, Epiphyas postvittana, from areas that had been subjected to large-scale spraying of Btk for control of an exotic pest species. Btk was also detected in moths from isolated traps at c. I km from the treated area, but not in moths from traps at greater distances. These results indicate that Bt preparations could be used to mark naturally occurring populations as well as laboratory-reared individuals to study their dispersal.