Strawberry blossom weevil Anthonomus rubi Herbst (Col.: Curculionidae): relationships between bud damage, weevil density, insecticide use, and yield

The activity of overwintered strawberry blossom weevils, Anthonomus rubi Herbst, measured as cut buds and adult weevils, was recorded weekly in sprayed and unsprayed quadrats in young and old strawberry plantings. The study was done in nine ‘Korona’ fields in a district with high A. rubi density, in the southeast of Norway, in 2000. During the period of study, the cumulative number of cut buds and adult weevils found by tapping whole plants above a bowl were highly correlated. An increase in sampled weevils was followed by an increase in cut buds 1–2 weeks later. Thus, sampling adults has potential for predicting the bud damage. In five of the six fields where yield was measured, a negative relationship between cut buds and the saleable yield was found. The effect of spraying was relatively low: A. rubi activity was reduced by 21% and the saleable yield increased by 16%. We conclude that present spraying practices are not very efficient in preventing A. rubi damage in the area studied.