Cocoon predation on diprionid sawflies: the effect of forest fertility |
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Authors: | Jari Kouki Päivi Lyytikäinen-Saarenmaa Heikki Henttonen Pekka Niemelä |
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Institution: | (1) Faculty of Forestry, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland e-mail: jari. kouki@joensuu.fi, Fax: +358-13-2514444, FI;(2) Department of Ecology, Lund University, S-223 62 Lund, Sweden, SE;(3) Finnish Forest Research Institute, PO Box 18, FIN-01301 Vantaa, Finland, FI |
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Abstract: | Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested
that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of
environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly
species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years
later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that
forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility
of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced.
N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is
important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season
than on the fertility of the forest site.
Received: 1 March 1998 / Accepted: 25 May 1998 |
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Keywords: | Predation Forest site Diprion Neodiprion Fertilization |
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