Spring dispersal of Sitona lineatus: the use of aggregation pheromone traps for monitoring.
The spring dispersal of the curculionid Sitona lineatus was investigated on a Danish farm during April-June 1987. Adults dispersed by flight in the early spring on sunny, calm days with temperatures above ca. 15°C. Two thirds of the population dispersed from perennial leguminous crops (clover [Trifolium] and lucerne) in the 1st period of flight activity. The next dispersal did not occur until 1 month later despite several intermediate flight activity periods. The 1st period of dispersal occurred before the germination of the spring sown summer host crop, Vicia faba [faba beans]. The bean crop was infested in 3 later invasions during a period of more than 3 weeks. The aggregation pheromone, 4-methyl-3,5-heptanedione, had a significant effect on captures of both males and females in cone traps placed on the ground. There was no effect of the pheromone on captures in yellow sticky traps placed 1.5 m above ground. The pheromone cone traps were highly specific whereas all kinds of flying insects were caught in the yellow sticky traps, thus making the latter traps less suitable for monitoring.