Effects of reduced pesticide dosages on carabids (Coleoptera: Carabidae) in winter wheat

1 The effects of reduced insecticide and herbicide dosages on total dry mass of carabids and their generic components were examined using fenced pitfall traps in winter wheat fields on three farms in Southern Zealand, Denmark. 2 The estimated total dry mass of carabids increased by 25% when the pesticides were reduced to one fourth of the normal application rates. 3 At reduced dosages, the activity of the genus Pterostichus was increased by 62%. The activities of Loricera and Demetrias were increased by 67% and 56%, respectively, although significant interaction terms indicated that the dosage effect was not uniform for these genera on all farms. Calathus tended to be more numerous with reduced pesticide applications. By contrast, catches of Bembidion, Synchus and Trechus decreased by up to 45% at reduced dosages. 4 A higher weed cover due to reduced herbicide applications probably benefited most species, except those having habitat associations with sparse vegetation such as the field-inhabiting Bembidion and Synchus. 5 The higher activity of larger carabids may lead to enhanced predation on smaller carabids and hence different carabid assemblages.