Recruitment of adult Colorado potato beetles in Bt-transgenic potato fields

A refuge of conventional potato plants adjacent to Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say)-resistant, Bt-potato (transgenic) plants may reduce opportunity for the development of tolerance to the resistant plants. The refuge strategy was developed on the basis of data available for CPB recruitment in conventional potato fields. This study was undertaken to provide information on CPB recruitment in Bt-transgenic potato fields. A marking experiment was conducted over the 2000 and 2001 crop seasons to determine the relative contributions of beetle populations from fields 10 in, 175 to 300 in, and 1200 to 1280 in distant to the pattern of CPB recruitment (immigration) in a Bt-potato field. Season-long CPB recruitment in the Bt-potato field decreased with source distance in a manner similar to that previously reported in conventional potato fields. Although marked beetles from the 10-m field plot contributed more to the recruitment than the more distant fields, they contributed only 3.3% and 6.6% of the total beetle sightings in the Bt-potato field. Therefore, results suggest that a larger acreage of conventional potato fields at some distance from the resistant crop could replace the adjacent designated refuge. Seasonally, beetles from the overwintering sites provided the first recruits to the resistant field. As their contribution declined, the overwintered beetles from the refuge were recruited until the beginning of the summer population. These results suggest that locating the resistant fields close to active overwintering sites will improve the probability that the refuge strategy will be effective by ensuring the presence of recruits at the very beginning of the crop season. The substantially lower recruitment level obtained for summer than for overwintered CPB in resistant and conventional potato fields highlights the need to reconsider the applicability of the refuge strategy for the summer population.