Sawflies in the crowns of native and exotic trees, sampled with flight-interception traps in southern Germany (Hymenoptera : Symphyta)

摘要

Hymenoptera: Symphyta were sampled at four locations in southern Bavaria (Germany) using flight interception traps, as part of a wider survey of flying insects in the crowns of four native tree species (Picea abies (Linnaeus 1753) Karsten, Abies alba Miller 1768, Fagus sylvatica Linnaeus 1753, Quercus robur Linnaeus 1753) and two exotic species (Pseudotsuga menziesii (Mirbel 1825) Franco, Quercus rubra Linnaeus 1753). Results agreed with the few previous studies of European canopy faunas, in that Symphyta were found to be very scarce. The possible reasons for this scarcity are discussed. Numbers of sawfly species and individuals caught were highest on Q robur, followed by A alba and P abies and then the two exotic tree species. No sawflies were caught on F sylvatica. The relative importance of Q robur for adults of sawfly species, apart from its role as a larval host for some of these, is highlighted. Sawflies were nearly absent from Quercus rubra, indicating a low degree of acceptance of this exotic plant by native Symphyta. The small number of Symphyta captured on P abies was surprising,. and may be related to the favourable vitality of the stands investigated. Of the sawfly species sampled, Cephalcia alashanica Gussakowskij 1935 and Pleroneura dahlii (Hartig 1837) are probably mainly confined to the canopy stratum.