The pea weevil Sitona lineatus L. colonises pea fields sporadically in spring and damages the pea root system. To increase efficiency of insecticide treatments against this weevil, its temporal dynamics, spatial distribution and the effect of treatments were studied using traps and an aspirator. Pea weevils appeared at pea emergence, i.e. 47 degree-days after sowing. The temperature of 8°C served as development threshold and minimum and maximum daily values were used for temperature accumulation. Weevil distributions in fields were aggregated, but at no time any gradient was observed. Treatment had only small effects and the treated plot was quickly re-infested. Due to the high mobility of pea weevils, non-treated control plots required by Swiss regulations need to be monitored during the week following treatments.