by Marie-Claude Boileau | 2 June 2020
Published in Canadian Journal of Forest Research 28: 729-736
The effect of nutrient addition (fertilization with N, P, and K at a rate of 448, 224, and 224 kg.ha-1, respectively) on height growth, root biomass, leaf area, and foliar nutrient concentrations of slow-growing layers and newly planted seedlings of black spruce (Picea mariana (Mill.) BSP) was evaluated on an apparently productive mesic site in Québec. Annual height growth increment of fertilized layers was greater than 20 cm.year-1 compared with 3-4 cm.year-1 for the other three treatments. Fine root biomass (<2 mm in diameter) and leaf area growth were significantly higher for fertilized layers and seedlings compared with their respective controls. For both current and 1-year-old needles, foliar N concentration on a unit leaf area basis increased significantly for both layers and seedlings, and vector analysis showed that, in aIl cases, N was the most limiting nutrient. Five growing seasons after treatment, the only residual effect of fertilization on foliar nutrient concentrations was higher foliar N in fertilized seedlings. Thus, it appears that the slow growth of the unfertilized layers on this site was due to resource limitation rather than to the type of regeneration as such.
by Audrey Verreault | 2 June 2020
Published in The Canadian Entomologist 130: 201-214
Reproductive processes in female Pissodes strobi (Peck) fed with a 5% ground bark artificial diet following summer emergence were studied. Females exposed to different temperature and photoperiod regimes were dissected every other week and their reproductive organs were observed to evaluate the maturation time according to the treatments. After 12 weeks, half the females were transferred onto lateral branch sections of white pine and the other half onto artificial diet supplemented with 10% ground bark of white pine, and their realized fecundity was determined. During the first 12 weeks, ovary development was detected but very few mature oocytes were found. No significant differences were observed for the maturation times between the different abiotic conditions used, but significant differences were observed in female egg-laying response on natural and artificial diets. Females that completed their sexual maturation at 24oC and 16L:8D laid over a 3-week period 14.4 ± 8.8 (mean ± SE) and 2.6 ± 2.6 eggs per female on white pine sections and artificial diet, respectively. Oviposition behaviour was compared with results from an earlier experiment conducted with spring-emerging white pine weevils on natural and artificial substrates. The egg-laying responses on white pine seedlings and on an artificial diet with a concentration of 15% ground white pine bark were 0.892 ± 0.124 and 0.171 ± 0.394 eggs per female per day, respectively.
by Audrey Verreault | 2 June 2020
Published in The Canadian Entomologist 131: 725-727. doi: 10.4039/Ent131725-6
The spruce budworm Choristoneura fumiferana (Clem.) is the most damaging insect of the balsam fir Abies balsema (L.) Mill. (Pinaceae) and the white spruce Picea glauca (Moench) Voss (Pinaceae) throughout eastern North America. In outbreak conditions, close to 100% tree mortality can occur in untreated mature fir stands (MacLean 1980). Bacillus thuringiensis var. kurstaki (Bacillaceae) is currently used to reduce spruce budworm damage (Van Frankenhuyzen and Payne 1993). Other possible biological control agents, such as baculoviruses, are also investigated to complement the use of B. thuringiensis. Baculoviruses are advantageous because they occur naturally in several insect species and are generally host specific (Federici 1993).
by Marie-Claude Boileau | 2 June 2020
Published in Canadian Journal of Forest Research 29: 1-8
Growth and physiology of layers versus naturally established seedlings of boreal black spruce (Picea mariana (Mill.) BSP) were compared 15 years after a cutover in Québec. During the first 8 years, height growth of seedlings was greater than that of layers, averaging 10.4 and 7.0 cm/year, respectively. For the last 5 years, annual height growth of layers and seedlings did not differ (25 cm/year; p > 0.05). Over the entire 15-year period, total height growth of seedlings (251 cm) was greater than that of layers (220 cm), although total height did not differ (p > 0.05) over the last 6 years. During the 15th growing season, there were no differences (p > 0.05) for predawn shoot water potential, stomatal conductance, net photosynthesis, intercellular to ambient CO2 ratio, water use efficiency, and hydraulic conductance between layers and seedlings. For diurnal shoot water potential, seedlings showed slightly less stress than layers on two of the four sampling dates. Thus, in the first few years following the cutover, the slower growth observed for layers indicated that they had a longer acclimation period following the cutover. Afterwards, similar height growth, total height, and physiological characteristics of the two regeneration types indicated that layers can perform as well as naturally established seedlings.
by Audrey Verreault | 2 June 2020
Published in The Canadian Entomologist 131: 779-786
A laboratory experiment was conducted to identify the overwintering stage of the fir coneworm, Dioryctria abietivorella (Grote), in eastern Canada and determine the influence of photoperiod on diapause induction. ln another experiment, different developmental stages were exposed to field conditions to evaluate their capacity to survive the overwintering period. lnsects were either placed in the duff or exposed to ambient (above ground) conditions to assess the importance of overwintering site on winter survival. Exposure of the fir coneworm to constant short-days or a daily decreasing photoperiod during larval development induced almost all insects to initiate diapause at the fifth instar. Third-, fourth-, and fifth-instar larvae survived the overwintering period when placed in the duff. Because the fir coneworm must leave its host tree and drop to the ground to avoid rigorous winter conditions, we concluded that only fifth-instar larvae couId resume development in spring using such a strategy.
