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Qualitative Changes in [,eaves and Larval Growth
Leaf"toughness, like leaf"density, decreased following clipping of the leaves: it was only 85.7% of the control the
year following the 1 year treatment and 69.8% of the control after the 2 year treatment (Fig. 6). Nitrogen content was almost
the same in untreated trees tot 3 years (1991-1993) but decreased after leaves were clipped. It was 2.23-2.26% before the
treatment, 2.00-2.05% the year following the 1 year treatment (ca. 10% reduction), and 1.88% the year following the 2 year
treatment (16.6% reduction) (Fig. 7a). The N content following the 1 year treatment was almost the same in 1992 and 1993.
These results clearly indicate that nitrogen content is reduced by defoliation and is influenced not by the year but by the
degree of defoliation. Tannin content, however, increased the year following leaf clipping (Fig. 7b). When 2 mg of BSA was
added, about 0.4 mg of the protein was precipitated in the regimes of 2 year treatment and 1 year treatment, although precipitation
was not detected in the control regime. Furthermore, when 3 mg of BSA was added, no precipitation was recognized
in the 1 year treatment or the control regimes, but 0.43 mg of the protein was precipitated following the 2 year treatment.
These quantitative and qualitative changes in beech following defoliation support that the trees were less vigorous after
defoliation, and also less suitable for herbivores because of the declining nitrogen and increasing tannins.
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140
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Figure 6._Leaf toughness of beechleavesin the year following artificial defoliation. The number is a mean value, bar
means maximum and minimum value, and upper and lower sides of box are one standard error.
Survivorship rates on beech saplings were determined using the number of hatched larvae as a base. The x-axis in
Figure 8 is the number of days following egg attachment on June 30th. Although approximately half of the larvae reared on
the control saplings survived to maturity, only about 10% of those reared on the 2 year treatment trees survived to maturity.
Many of the latter died during early stages of larval development. Survivorship on the 1 year treatment was intermediate
between the 2 year treatment and the control. Both female and male body size declined for larvae reared on clipped saplings,
as did adult body size (Fig. 9). In the 2 year treatment regime, body size was smaller than of the 1 year treatment regime, and
was just three quarters of that in the control. Defoliation lowers beech quality which, in turn, lowers larval survivorship and
body size.
Population Quality of Herbivore in Three Sites
Test for Maternal Effects and Food Deterioration in the Field
The larvae from Site A had smaller body size (p < 0.01 t-test) than those from the other two regions (Fig. 10). This
tendency was exactly the same for males and females, as well as for mature larvae and for pupae. No difference was found
between the Site B and C populations. Thus it can be said that even three generations after an outbreak, the quality of the
Site A population was less than that of the populations from the other two regions where density was increasing.
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