The impact of the pea and bean weevil, S. lineatus, on field beans, V. fuba, was investigated in field cage experiments with controlled attack levels. A decrease in yield up to 28 YO was recorded due to a reduction in the number of pods per plant, whereas the number of seeds per pod and the individual seed weight were unaffected.As the damage was a non-monotonous function of the attack level, the experiment suggests a complex relationshi between attack level and yield loss due to adult weevils feeding on the leaf margins and larvae feeding on the root nodules.The number of larvae shortly before hatching was independent of the adult attack level, as the same numbers of larvae were found in all treatments, thus indicating an increasing mortality at higher population densities. Difficulty of establishment in suitable root nodules and intraspecific competition are considered to be the most important mortality factors.The complex relationship between the attack level and the yield response is discussed in relation to the density dependent mortality of the larvae. A significant correlation between attack level and the number of leaf margin feeding notches following infestation was recorded. This is discussed in relation to monitoring and warning.

The spring dispersal of Sitona lineatus L. (Coleoptera; Curculionidae) was investigated on a Danish farm. S. lineatus dispersed by flight in the early spring on sunny, calm days with temperatures above ca. 15 °C. Two thirds of the population of S. lineatus dispersed from perennial leguminous crops (clover and lucerne) in the first period of flight activity. The next dispersal did not occur until one month later despite several intermediate flight activity periods. The first period of dispersal occurred before the germination of the spring sown summer host crop, Vicia faba L. The field bean crop was infested in three later invasions during a period of more than three 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 effect is discussed in relation to behavioural observations. Both types of traps may be used in a survey system for monitoring spring dispersal of S. lineatus and optimal timing of insecticide spraying. However, 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.

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