Susceptibility of silver fir (Abies alba) trees, affected by decline, to attack by cone and seed insect pests. Preliminary results.
A study was conducted within two silver fir (Abies alba) stands in Romania, located at altitude 480 m and 501 m and affected by forest decline. The study was conducted during an abundant cone crop year. On 24th July 1997, cones were collected from trees with different degrees of decline. Within both study plots, all important insect pests of silver fir cones and seeds were identified: Resseliella piceae (Diptera: Cecidomyiidae), Earomyia impossibile (Diptera: Lonchaeidae), Barbara herrichiana (Lepidoptera: Tortricidae) and Megastigmus suspectus (Hymenoptera: Torymidae). Resseliella piceae was the dominant species, infesting up to 92% of cones, but the most serious pest was Barbara herrichiana, which damaged up to 6.3% of seeds. All species, except Megastigmus suspectus, preferred cones from healthy trees or those only slightly affected by decline: it is postulated that M. suspectus may be operating behaviour aimed at diminishing competition with other pest species, rather than being attracted to cones from severely affected trees. However, cones from severely declining trees had fewer fertile seeds, because the proportion of empty seeds was higher compared to that of cones from healthy trees.