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Figure 1.---Locations of beech forests which have had been conspicuously defoliated by Q. punctatelIa (dark shading), and
three study sites: Hakkohda (Site A), Hachimantai (Site B), and Appi (Site C).
Estimation of Larval Density
The density of Q. punctatella in each plot was estimated by trapping frass pellets of the last instar larvae, because
defoliation is mostly the result of its feeding (Kamata and Yanbe, 1993). The density can usually be estimated by the
following equation: Density = Total number of frass pellets per square meter/630, where 630 is mean number of frass
pellets during last instar stage. Because density is underestimated when larval density becomes high and conspicuous
defbliation occurs, the density must be calculated by the following equation: log,0 (Density) = 0.988"1og,0 X + 0.898,
where X is the maximum number of frass pellets per day per square meter (Kamata and Igarashi, 1994a).
Adult Number and Size
Adult numbers were measured at Site B. Two light traps were set in an open area in a small valley surrounded by a
forest of predominantly beech. The distance between the two traps was 10m and both were 20m from the nearest edge of
the beech forest where the heaviest defoliation had occurred in a 1981 outbreak. Each light trap had two blue fluorescent
bulbs (20W) and a basin with water and kerosene. The relative numbers were estimated by the total catches during the
20 days from June 1lth to 30th, because the peak of the adult catches was in mid- to late June (Kamata and Igarashi,
1994). Body size of the adult greatly influenced fecundity, but the fecundity of a trapped female cannot be estimated
directly or indirectly from body weight, because both measurements decrease rapidly after emergence due to oviposition
(Kamata and Igarashi 1995a). Rather, the area of forewing, which showed a good correlation with both fecundity and
adult weight, was used as a substitute measurement of body size and fecundity (Kamata and Igarashi 1995c). The area
was therefore measured by digitizer to the nearest mm z and its annual change was compared with population dynamics.
In Site A, one light trap, which had two blue fluorescent bulbs (20W) and no basin, was set in a bare area ca. 20 m apart
from the edge of beech forest completely defoliated in 1990. A sheet of white, finely-meshed cotton cloth (1.8m x 1.8m)
was set behind the trap and adults were caught on it. This survey was conducted several days each year from 1988 to
1993. Area of the beech caterpillar's forewing was also measured. 69
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