Associations among parasites of Populus

JONES, B., and NEWCOMBE, G. 1999. Associations among parasites of Populus. Can. J. For. Res. 29: 00-000. Two related F2 families of a Populus trichocarpa x P. deltoides hybrid pedigree were examined in the field for the presence of parasites (three fungal pathogens and five arthropod herbivores), during the third and fourth years of tree growth. The null hypothesis of no associations among parasites, was tested using a method suggested by a test for associations among species colonizing islands. In our case, the method was simplified by the fact that we did not place any restrictions on the number of parasites that can infect a given tree (tree ≅ island). A negative association was discovered between Glomerella cingulata and a species of Taphrina, two fungal pathogens, as there were significantly fewer than the expected number of co-occurrences in the third year, and none in the fourth. Another negative fungus-fungus association was evident in the fourth year between Taphrina and Venturia populina. A positive insect-insect association between a Gracillariid leaf miner and Phyllocolpa bozemani, a leaf-folding sawfly, was observed in both years. Another positive association was observed in the fourth year between the fungus Glomerella cingulata, and an eriophyid mite, Schizoempodium mesophyllincola.