Resistance of seven fir species to spruce budworm and other insects.
In June 1971, the susceptibility of seven species of fir (Abies) to attack by larvae of Choristoneura fumiferana (Clem.) was investigated in the field and laboratory in New Brunswick, Canada, in relation to the date of needle flushing of the trees [cf. RAE/A 62, 5200, etc.]. On field-collected samples of balsam fir (A. balsamea), white fir (A. concolor), Siberian fir (A. sibirica) and grand fir (A. grandis), in which the first flush was 0-8 days after that of balsam fir, the dry weight of larvae averaged 8.1-10.1 mg, and most larvae were in their final instar. On Korean fir (A. koreana), Fraser fir (A. fraseri) and Nikko fir (A. homolepis), in which the first flush was 18-39 days after that of balsam fir, the dry weight averaged 2.2-3.4 mg and most larvae were in the fourth-fifth instar. Larval behaviour is described in relation to the state of development of the buds and foliage. The later-flushing species appeared more resistant to attack by the aphid Mindarus abietinus Koch. The suitability of the different species for planting (especially for sale as Christmas trees) is discussed in relation to their appearance, and susceptibility to attack by C. fumiferana, M. abietinus, Dasineura balsamicola (Lint.) [cf. 62, 5196], Adelges piceae (Ratz.) and Hemerocampa (Orgyia) leucostigma (J.E. Smith).