Vulnerability of the fir coneworm, Dioryctria abietivorella (Grote) (Lepidoptera: Pyralidae), in different larval stages to the HD-1 strain of Bacillus thuringiensis
Published in The Canadian Entomologist 129: 197-198
Initial size and competing vegetation effects on water stress and growth of Picea mariana (Mill.) BSP seedlings planted in three different environments
Published in Forest Ecology and Management 103: 293-305
Three experimental sites in Québec were planted with four different sizes of containerized black spruce seedlings (Picea mariana (Mill.) BSP). We examined the water stress experienced by each stock size of black spruce seedlings in relation to different competing vegetation covers and also the effect of the water stress on spruce growth during the first three growing seasons. The sites consisted of one abandoned agricuItural field and two forest locations. Containers of sizes 45-110, 45-340, 15-700, and 12-1000 were employed to produce the four different sizes of spruce seedlings. At each site, the experimental protocol used a split-plot in a randomized complete block design, in which the presence of a competing vegetation cover (weedy and bare plots) was assigned to the whole plot, while a specific seedling size was assigned to each subplot. At each experimental site both the predawn xylem water potentiaI Yxp and the midday value Yxm were measured three times during each of the first three growing seasons. Data were analysed as a completely randomized split-split-plot design, where selection of seedlings in time was considered as the whole plot. The competing vegetation tended to protect the spruce seedlings from excessive water loss, without depressing the soil-water potential (SWP) to the point of reducing the moisture available to the seedlings. Both Yxp and Yxm were found to decrease significantly with increasing initial seedling size. The increased water stress experienced by the large stock of spruce seedlings had an effect on the absolute growth rate (AGR) in height on only one experimental site. The AGR was impaired by the presence of a competing vegetation cover, but more severely for the smaller stock-size than the larger. The short-term effect of a competition should be based on radial growth; height growth and mortality are not early indicators of such effect. These results emphasize the need to produce a large stock of spruce seedlings with well-developed root systems and root growth capacity, even though only moderate water stress was observed during the first three years of plantation growth.
Nutrient status and growth of black spruce layers and planted seedlings in response to nutrient addition in the boreal forest of Québec
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.
Gonadal development and egg-laying response of female white pine weevils reared on artificial and natural diets
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.
Pathogenicity of a granulovirus towards Choristoneura fumiferana (Lepidoptera: Tortricidae)
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).
