View or print this publication - Northern Research Station - USDA ...

Defoliation Experiments
To test the food deterioration hypothesis, the growth of larvae reared on beech saplings which had suffered previous
artificial defoliation wascompared with controls. It was assumed that the effects of defoliation would be apparent in mid
August. Treatments were a 2 year regime where all leaves were clipped for 2 years running in 1991 and 1992. Another
regime was a single year treatment during which all leaves were clipped for only the year (1992) prior to the experiment. No
clipping was done in thecontrol group. Q. punctatella were reared in screened enclosures on branches of treated and control
beeches. Larvae were occasionally shifted from one branch to another so that food was always plentiful. Survivorship and
mature body size were compared by rearing the larvae to maturity on these saplings. The Q. punctatella used in the experiment
originated from a population on Site A three generations after the previous outbreak.
Testsfor Food Deterioration and Maternal Effects Hypotheses in the Field
Three different regional Q. punctatella populations were reared on beech trees in the Tohoku Research Center of the
Forestry and Forest Products Research Institute in Morioka to evaluate population quality (Fig. 1). Larvae were reared in
screened enclosures on branches and mature body sizes were compared.
Eggs collected from these three regions were attached to beech saplings in each region. Larvae were also reared in
screened enclosures on branches, and survivorship and mature body size compared among the three. From these results the
influence of I_ostand herbivore quality on population dynamics and associated changes in body size were determined.
Quantitative and Qualitative Properties of Beech Leaves
_Ik)learn about changes in leaves which had been defoliated, their number and dry weight were determined. Dry
weight of l0 leaf disks (2 cm in diameter), one punched from each of 10 randomly selected leaves, was viewed as an index of
leaf density. Decrease inthe weight and the density of a leaf were compared to determine how leaves change due to defoliation.
Leaf toughness wasalso measured using a "penetrometer" as described by Feeny (1970).
We used the protein-precipitation assay as a measurement of the tannins. We measured the precipitation of BSA by
extracts of beech leaves according to Martin and Martin (1983) and Makkar et al. (1987). Leaf powder (150 mg) was
extracted three times with 3 ml of 70% acetone, and the total volume of the combined solution of extracts was adjusted to 10
ml with the solvent. One ml of the above stock solution from leaf powder was added to 2 ml or 3 ml of 0.1% BSA solution
(containing 2 mg or 3 mg of BSA, respectively) in acetate buffer (pH=5.0). The amount of precipitated BSA was determined
by ninhydrin assay.
RESULTS
Population Dynamics and Body Size
Larval densities changed with the same pattern in all three areas (Fig. 2). Density was lowest in 1986, and increased
successively until 1990 (Kamata and Igarashi 1995c). In Site A, slight defoliation was recognized in 1989 and heavy
defoliation in 1990. The predator, Calosoma maximowiczi (Coleoptera, Carabidae), and an entomopathogenic fungus,
Cordyceps militatis (Clavicipitales: Clavicipitaceae), greatly increased in abundance during the outbreak periods (Kamata
and Igarashi 1994c, Sato et al. 1994). The densities in Sites B and C were not as high in 1990, and neither defoliation nor
natural enemies were conspicuous. However, the density decreased in 1991 in all three areas, then increased again in 1992.
The resilience of the population density in 1992 was stronger in Sites B and C, where natural enemies were not conspicuous
in 1990, than in Site A.
Moth numbers in Site B fluctuated in tandem with larval density (Fig. 3). They were lowest in 1987, then increased.
Interestingly, moth numbers were almost the same in 1990 and 1991, though the larval density decreased in 1991. Adult
number began to decrease after 1992.
70