Impact of cocoon predation and parasitism on endemic populations of the common pine sawfly, Diprion pini (L.) (Hymenoptera, Diprionidae) in different forest types
1 Predation and parasitism on litter-buried cocoons of the common pine sawfly Diprion pini (L.) were compared in different forest types with endemic sawfly populations by field exposure of laboratory-reared cocoons during three consecutive years (1993–1995).
2 The impact of cocoon predation was dependent on season and forest type. The highest predation (up to 95%) was found during autumn in forest stands with a dense understory vegetation.
3 Cocoon parasitism varied between year, season and forest type. The highest parasitoid attack was observed in pure pine forests with more or less barren soils, but did not exceed 24% of exposed cocoons.
4 Cocoons were exposed in small patches. Predators tended to exploit all cocoons of a patch, whereas parasitoids only attacked a few cocoons of a patch. Predation was similar on cocoons placed in the litter and those buried more deeply in the soil, whereas parasitism of soil-buried cocoons was rare.
5 These results indicate that predators can have a remarkable potential for limiting endemic sawfly densities, if habitat conditions in a forest maintain their population and support their foraging behaviour. A notable effect of parasitoids on sawfly cocoons deposited in the litter is obviously restricted to typical pure and barren pine forests, but may play there a similar role as predation.
Document Type: Research Article
Affiliations: Lehrstuhl für Tierökologie, Forstwissenschaftliche Fakultät, Technische Universität München, Am Hochanger 13, D-85343 Freising, Germany
Publication date: 2003-02-01