Pyrethroid resistance and thiacloprid baseline susceptibility of European populations of Meligethes aeneus (Coleoptera: Nitidulidae) collected in winter oilseed rape.

BACKGROUND: Pollen beetle, Meligethes aeneus F. (Coleoptera: Nitidulidae), is a major pest in European winter oilseed rape. Recently, control failures with pyrethroid insecticides commonly used to control this pest have been reported in many European countries. For resistance management purposes, the neonicotinoid insecticide thiacloprid was widely introduced as a new mode of action for pollen beetle control.
RESULTS: A number of pollen beetle populations collected in Germany, France, Austria, Great Britain, Sweden, Denmark, Finland, Poland, Czech Republic and Ukraine were tested for pyrethroid resistance using lambda-cyhalothrin-coated glass vials (adult vial test). Most of the populations tested exhibited substantial levels of resistance to lambda-cyhalothrin, and resistance ratios ranged from < 10 to > 2000. A similar resistance monitoring bioassay for the neonicotinoid insecticide thiacloprid was developed and validated by assessing baseline susceptibility data for 88 European pollen beetle populations. A variation of less than fivefold in response to thiacloprid was detected. The thiacloprid adult vial bioassay is based on glass vials coated with an oil-dispersion-based formulation of thiacloprid, resulting in a much better bioavailability compared with technical material. Analytical measurements revealed a > 56 and 28 day stability of thiacloprid and lambda-cyhalothrin in coated glass vials at room temperature, respectively. No cross-resistance between thiacloprid and lambda-cyhalothrin based on log-dose probit-mortality data was detected.
CONCLUSION: Pyrethroid resistance in many European populations of M. aeneus was confirmed, whereas all populations are susceptible to thiacloprid when tested in a newly designed and validated monitoring bioassay based on glass vials coated with oil-dispersion-formulated thiacloprid. Based on the homogeneous results, it is concluded that thiacloprid could be an important chemical tool for pollen beetle resistance management strategies in European winter oilseed rape.