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1985 1986 1987 1988 1989 1990 1991 1992 1993
Year
Figure 3.--Number of Q. punctatella adults caught in two light traps in Site B (Hachimantai) 1985-1993. The number of
adults of each sex in each trap is shown. Nitrogen content of foliage was measured by a CHNS/O Analyzer
(Perkin-Ehner PE2400 Series II) to the nearest 0.01%.
Body size of moths gradually increased with larval density, but decreased suddenly in 1991 in Site A where severe
defoliation had occurred the previous year (Fig. 4). A quantitative food shortage in 1990 was probably the main factor
causing this size reduction. Body size increased a bit but was still small in 1992 and 1993, but larval density decreased and
no food shortage occurred after 1991. Thus, factors other than a shortage of food were involved in the size decrease. Because
size was ahnost the same in the two sites before the outbreak, the great difference between the two after the outbreak
was not genetically determined.
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