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solely to the outbreak generation. Many insects have been shown to have body size changes associated with their population
density dynamics. In other words, during a period when population density is increasing, body size also increases, and the
reverse occurs when population density is declining, body size decreases also (Baltensweiler and Fischlin 1988, Myers 1990),
In Q. punctatella, body size changed in the same way as the density. Changes in fecundity caused by these changes in body
size were probably one factor causing the population fluctuation.
Because the body size of Q. punctatella at Site A before the outbreak was approximately the same as that for the Site
B population, the current small body size of the former is thought not to be genetically determined. Body size at Site A
dropped to 70% of the norm the year following the outbreak and was 80% even two generations after the outbreak. This
cannot not be explained solely by a lack of food during the outbreak. The results indicate that beech which has experienced
de_i)liation the previous year is a poor host, causing both survivorship and body size of larvae to decline. Even though 3
years had passed since the outbreak at Site A, larvae reared on Site A beech still had low survivorship. Corresponding to host
quality, Q. punctatella quality was still bad in Site A. Even when Q. punctatella populations from this site were reared on
beech from the other sites where density was increasing, the bodies of these larvae were still significantly smaller. High
mortality, due to deterioration of food and small body size, and low egg production due to poor Q. punctatella quality,
explains why its density continued to decline years after the outbreak. Several authors have demonstrated that poor nutritional
status in one generation may deter normal development in the next. Examples include Lymantria dispar (Kovasevic
1956), Malacosoma pluviale (Wellington 1965), and Hyphantria cunea (Morris 1967). Such intergenerational, cumulative
effects are called "maternal effects" (Rossiter 1992). Rossiter (1992) states "maternal effects are the result of resource
provisioning by one generation for the next... The resource based maternal effects are the product of gene-environment
interactions experienced in the parental generation." Deterioration in Q. punctatella quality after the outbreak was the very
result caused by maternal effects.
Haukiojia and Neuvonen (1987) proved the hypothesis that poor food may select for individuals with superior ability
to process low-quality diets. However, experiments conducted here did not confirm this: the survivorship of Site-A Q.
punctatetla was significantly lower than that of Site C Q. punctate[la, and was almost the same as that of Site B Q.
punctatella on poor-quality Site A beech.
Concerning the food deterioration hypothesis, it is necessary to distinguish between induced changes in secondary
compounds such as tannin, which are an active means of defense (induced defense hypothesis) and that of passive changes in
secondary chemistry following episodes of defoliation (Myers 1988). The defense strategy of beech, in relation to severe
defoliation, changed as time passed after an outbreak, though in each case it resulted in high mortality and small body size of
Q. punctatella. In the year following defoliation, beech became less vigorous and the defense response was a passive one
(food deterioration): tannins increased and nitrogen content decreased. Next, trees became more vigorous and the defensive
strategy changed to a more active one; both nitrogen and tannin content increased.
The results on Site B beech were unexplainable by this scenario; nitrogen content was lower than Site A beech and
tannin content was almost the same, but the tree performance was comparable to Site C beech for rearing Q. punctatella.
These results indicate that it is very dangerous to discuss the performance of plants by measuring only nitrogen or secondary
compounds. Clancy (!99 l) also demonstrated that Douglas fir trees susceptible to the western spruce budworm had lower
levels of foliar nitrogen and sugars than resistant trees, and that the susceptible trees had mineral/nitrogen ratios which were
closer to optimal levels. Not only secondary compounds such as phenols and tannins but also minerals thus must be taken
into consideration.
Nitrogen content in untreated trees at Site A was nearly the same in all 3 years (1991-1993) and that in beeches
following 1year of defoliation was the same for 2 years (1992-1993). It differed greatly among the three sites, but variance
within a site was very minimal. Beech leaves at outbreak Sites A and B showed higher nitrogen content than at the nonoutbreak
Site C. There is a possibility that nitrogen level is linked to the site dependent outbreak characteristics of Q.
punctatella.
The induced defense hypothesis advocates the following scenario. Due to the decline in food quality after an
outbreak, succeeding generations decline, that is, insect growth is checked and population numbers decrease. With the
recovery of plant quality, insect population density begins to increase again, thus creating the cyclical population dynmnic:s
of these insects. Two different types of beech response were recognized in the decline in food quality as time passed afte:r an
outbreak (Fig. 13). Beech becomes less vigorous soon after severe defoliation, and nitrogen content decreases but deferlsive
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