Harmfulness of mirid bugs (Heteroptera, Miridae) on hop plants

Mirid bugs in a high density were registered in some hop-yards in Czech Rep ublic in 1998. Harmful occurrence is usual in the years with higher tempera ture and length of sunshine connected with lower precipitation in the perio d from October to May. Mirid bugs cause the damage to hop veins, leaves and inflorescence. Vegetative cones are the: organs which are the most sensiti ve to mirid bugs. The symptoms of the damage are as follows: distortion, wi lting and top drying. The most common species inside those hop-yards and in their nearest vicinity are the polyphagous ones: Lygus kalmi, Lygus ruguli pennis, Lygocoris lucorum, Liocoris tripustulatus, Calocoris fulvomaculatus and Calocoris norvegicus. The yield of hop cones obtained from damaged pla nts was lower by 50.1% in the average per one hop plant in the comparison w ith undamaged plants.