RESISTANCE OF SCOTCH PINE VARIETIES TO ZIMMERMAN PINE MOTH (LEPIDOPTERA, PYRALIDAE) AND ITS IMPACT ON SALES IN A CHOOSE AND CUT CHRISTMAS TREE PLANTATION

Nine varieties of Scotch pine, Pinus sylvestris, were assessed for the ir susceptibility to Zimmerman pine moth, Dioryctria zimmermani, in a choose and cut Christmas tree plantation. Trees were examined for woun ds to estimate their susceptibility to this pest 7 years after plantin g in the field. Numbers of trees remaining after seasonal sales in yea rs 7 and 8 were used to estimate marketability of each variety. Infest ation rates varied significantly among varieties (11-75%). After sales , proportions of trees remaining also varied significantly among varie ties (7-52%). Although Belgian trees were the most moth resistant, the y were the least purchased by the public, probably owing to their yell ow-colored foliage. Excluding the Belgian variety, proportions of infe sted trees were positively related to the number of trees remaining af ter two years of sales (F = 12.7 df = 1,22, R-2 = 0.37, P<0.002). This linear relation suggested that in a population of 100 trees, three tr ees must be wounded to cause one not to be sold. This implies that app earance of advanced damage symptoms such as brown and broken branches have a greater negative impact on sales than the simple presence of wo unds.