Chalcidoid fauna (Hymenoptera: Chalcidoidea) of grasslands situated in rapeseed (Brassica napus L.) surroundings in Bulgaria

The objective of the current study was to assess the potential of semi-natural grasslands to serve as parasitoid sources from which individuals can spread to the surrounding cultivated habitats. The composition of chalcidoid fauna was studied in nine non-harvested grasslands located near to but not bordering oilseed rape (Brassica napus L.) fields. The investigated areas were generally used as pastures for domestic animals, but vegetation was not intensively grazed in all sampling sites. Samples were collected by sweep-netting during the period between full flowering and the end of flowering of the rapeseed (stages 65-70 according to the BBCH-scale). Insect counts showed significant dominance of Eulophidae Westwood (84 individuals; 42%) and Pteromalidae Dalman (60 ind.; 30%), with lower abundance of Eurytomidae Walker (22 ind.; 11%). Some other groups were poorly represented – Torymidae Walker (10 ind.; 5%), Encyrtidae Walker (9 ind.; 5%), Ormyridae Förster (6 ind.; 3%), Eupelmidae Walker (4 ind.; 2%), Chalcididae Latreille (2 ind.; 1%) and Tetracampidae Förster (2 ind.; 1%). Most numerous among eulophids were Baryscapus Förster (38 ind.; 46%), Aprostocetus Westwood (21 ind.; 25%) and Necremnus Thomson (11 ind.; 13%). Nine other genera comprised the remaining 23% of the eulophid collection – Diglyphus Walker, Elachertus Spinola, Entedon Dalman, Eulophus Geoffroy, Neochrysocharis Kurdjumov, Neotrichoporoides Girault, Pnigalio Schrank, Sympiesis Förster and Tetrastichus Haliday. The most abundant pteromalids were Mesopolobus Westwood (20 ind.; 37%) and Pteromalus Swederus (11 ind.; 20%), followed by 13 genera with 7% or less – Catolaccus Thomson, Chlorocytus Graham, Cyrtogaster Walker, Cyclogastrella Bukovskii, Gastrancystrus Westwood, Glyphognathus Graham, Halticoptera Spinola, Homoporus Thomson, Norbanus Walker, Psilocera Walker, Trichomalus Thomson, Spalangia Latreille and Systasis Walker. Parasitoid diversity and its possible beneficial role were discussed according to the present knowledge on the rapeseed pests and their natural enemies