Effects of thiacloprid, tau-fluvalinate and lambda-cyhalothrin on overwintered pollen beetles (Brassicogethes aeneus (Fabricius)) and their offspring in oilseed rape

To prevent damage by pollen beetles (Brassicogethes aeneus (Fabricius), syn. Meligethes aeneus (Fabricius)), frequent insecticide applications are often necessary. It would be an advantage if treatments for pollen beetle control would not only avoid yield losses by bud damage by overwintered pollen beetles, but also minimize pest reproduction, and also have side effects on the population development of other pests present in the crop. The effects of the neonicotinoid Biscaya (a.i. thiacloprid) and the pyrethroids Mavrik (tau-fluvalinate) and Karate Zeon (lambda-cyhalothrin) applied at different growth stages of winter oilseed rape on the abundance of overwintered pollen beetles were determined in field trials in Germany (2013–2015). In addition, effects on the two larval instars and new generation of adult pollen beetle were studied. Biscaya and Mavrik significantly reduced the number of overwintered pollen beetles up to seven days after application, whereas Karate Zeon had no effect. Application of Biscaya at the beginning of flowering resulted in a high mortality of L1-larvae in all years. The number of premature L1-larvae dropping down from the plants during the first week after application increased up to 425% compared to the control. The number of L2-larvae dropping down to the ground for pupation was significantly reduced by insecticide applications at different growth stages except for Karate Zeon. In Karate Zeon-treated plots, the number of L2-larvae dropping to the ground increased up to 42% compared to the control. In accordance with the reduced number of L2-larvae in Biscaya- and Mavrik-treated plots, fewer new-generation pollen beetles emerged in the field trials near Braunschweig, efficacy varying between 57 and 76% in Biscaya-treated plots and 32 and 57% in Mavrik-treated plots in 2014 and 2015, respectively. The results indicate that Mavrik, and especially Biscaya, are effective in controlling pollen beetles, reducing infestation pressure and thereby insecticide treatment frequency in following years.