Appendix A. A description of conversion of L2 density to egg-mass density.
Egg masses are counted by visually examining sample branches, whereas the second-instar larvae (L2) in hibernacula are counted after being extracted from sample branches soaked in a 1% NaOH solution that dissolves the hibernacula (so called "washing"). The debris containing larval body parts is spread out over a sheet of white filter paper marked with a grid, and is examined under a dissection microscope (Miller and Kettela 1972). The extraction efficiency (the proportion of L2 on a branch extractable by the method) and its consistency appear to depend on the particular washing procedure. Since 1985, the New Brunswick Department of Natural Resources has standardized the double-wash technique (Hartling 1994).
In 1984, the year before the L2 count replaced the egg-mass count, a few sample branches were collected (as described in section SURVEY SYSTEM) in the fall at each of 126 sampling sites distributed fairly evenly over the northern half of the province. These branches were processed by the standardized washing technique, which yielded an average of 247.8 L2 per 10 m2 of foliage surface area. In the meantime, the egg-mass counts in the same regions, that included 1095 sampling sites, yielded an average of 185.0 masses per 10 m2. As an egg mass normally contains, on average, about 20 eggs, the (egg masses / L2) ratio yields an approximate conversion factor of 0.75, i.e.,
Egg-mass density = 0.75 × (L2 density).
The constant conversion factor assumes that egg-to-L2 survival is largely unrelated to egg density. It also assumes that the proportion hibernating on foliated branches (to be sampled) does not depend on egg-mass density.
LITERATURE CITED
Hartling, L. 1994. Forecasting spruce budworm infestations--a historical review of field and laboratory procedures of overwintering (L2) larval surveys conducted by New Brunswick Department of Natural Resources and Energy from 1983 to 1994. Reference Document, New Brunswick Department of Natural Resources and Energy.
Miller, C. A., and E. G. Kettela. 1975. Aerial control operations against the spruce budworm in New Brunswick, 1952–1973. Pages 94–112 in M. L. Prebble, editor. Aerial control of forest insects in Canada. Catalogue No. Fo23/19/1975, Information Canada, Ottawa, Canada.