Population dynamics of the beech caterpillar, <Emphasis Type="Italic">Syntypistis punctatella</Emphasis>, and biotic and abiotic factors |
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Authors: | N Kamata |
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Institution: | (1) Department of Biology, Faculty of Science, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan Tel. +81-76-264-5708; Fax +81-76-264-5708 e-mail: kamatan@kenroku.kanazawa-u.ac.jp, JP |
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Abstract: | The beech caterpillar, Syntypistis punctatella (Motschulsky) (Lepidoptera: Notodontidae), often causes extensive defoliation of beech forests in Japan. Outbreaks have often
occurred synchronously among different areas at intervals of 8–11 years. Synchrony of outbreaks was considered to be caused
by synchrony of weather. Populations of this insect exhibit periodical dynamics in both outbreak and nonoutbreak areas. Factors
that might influence the population dynamics of the beech caterpillar were classified from the point of view of the natural
bioregulation com-plex, which includes a coleopteran predator, Calosoma maximowiczi, avian predators, parasitoids, entomopathogenic fungi, and delayed induced defensive response (DIR) of beech trees. Because
such periodic population dynamics are believed to be caused by one or more delayed density-dependent factors, delayed density-dependent
mortality has been identified as a likely source of population cycles. The DIR and pathogenic diseases showed a high order
of density dependence. An infectious pathogen, Cordyceps militaris, was considered to be the most plausible agent responsible for periodic dynamics of the beech caterpillar population because
insect diseases were effective in cases in which the S. punctatella population started to decrease without reaching outbreak densities, but DIR was not. Conspicuous defoliation caused by this
insect tends to occur at certain elevations, where forests are composed of pure stands of beech trees. I propose three different
hypotheses to explain this phenomenon: the diversity–stability hypothesis, the resource concentration hypothesis, and the
altitudinal soil nutrient hypothesis.
Received: November 20, 1999 / Accepted: August 3, 2000 |
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Keywords: | Quasi-periodic outbreaks Time delay Density dependence Insect disease Delayed induced response Site dependence |
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