Boletín de la AeE

The leafminer Chromatomyia fuscufa is an univoltine pest in cereals and grasses in Norway, but its parasitoid complex has been largely unknown. ín 1992 - ?_996 this complex was investigated in an organically managed barley fíeld and its surroundings at As, southern Norway, mainly by using leaf samples and Malaise traps. Results from the Malaise traps are presented. The traps were placed in the barley fíeld and (except 1994) at its boundary (either forest boundary or grass boundary) in May - November, the collecting period depending on habitat and year. The chalcidoid parasitoid species which we previously had reared from C. fuscula on barley (about 16 species) were sorted out.

The adult parasitoid number peaked rather late in the season, about two months after the leafminers invaded the barley fíeld. Although the number of specimens collected varied considerably from year to year (fíeld: 949 - 23617), the species complex had a rather stabile composition, with 14 -16 species each year. Of these species, 14 were collected every year, and 10 of these occurred both in the fíeld and at its boundary every year. The complex consisted of a few numerous species and many less common species. The dominant species in the fíeld alternated between the pupal parasitoid Cyrtogaster vttlgaris (Walker) (1993, 1995, 1996) and the larval parasitoid Diglyphus begini (Ashmeadj(1992 and 1994). In the boundaries, C. vulgoris always was the most numerous species in the complex. Each year, at least one of these two species also dominated the parasitoid complex that emerged from leaf samples infested with the leafminer.

The number of parasitoid species were similar in the fíeld and in the two types of boundaries, but O wlgaris showed a higher dominance in the boundaries coinpared with the fíeld. Most specimens were collected froin the grass boundary, followed by the fíeld and the forest boundary. The phenologv are shown for the leafminer and the most numerous parasitoid species.