S. Mahunka szerk.: Folia Entomologica Hungarica 61. (Budapest, 2000)

to the 40th day. Within this period the majority of the specimens of Potamia littoralis, Fannia scalaris, Lycoriella cellaris, Cecidomyiidae sp. 1, Coboldia fuscipes emerged. Finally, there is a third period from ca. the 40-42 day (seventh week), when Cecidomyiidae sp. 2 and Desmometopa sordida dominated the emerging adults, which were found in low numbers by that time. It is difficult and risky to say anything about the less abundant species but Tephrochlamys tarsalis seems to emerge in the intermediate period between the second and third ones, and Drapetis assimilis emerged in the last period. Twelve species are common in the two lists, which is a rather high overlap (the value of the Jaccard-index is 12/19 = 0.63). Although the two nests were not very far from each other (less than five air kilometres), two samples are too few for any generalisation; so below only remarks according to the dipterous species are given. Tephrochlamys tarsalis (Zetterstedt, 1847) (Heleomyzidae, or Heteromyzidae) was formerly known also from wasp's nests (Skidmore 1962). Eccoptomera obscura (Meigen, 1830) (Heleomyzidae) develops in small mammal burrows as well as in caves. Since Apodemus mice were active in the hollow No. 2, their emergence is not a surprise. New records from wasp's nests are for the following species: Tinearia alternata (Say, 1824); Coboldia fuscipes (Meigen, 1830) (very common in sporophores of fungi); Drapetis assimilis (Fallén, 1815), Gymnochyromyia inermis (Collin, 1933) (G. flavella (Zetterstedt, 1848), as G. minima (Becker, 1904), was reared from elm wood debris in Britain, see Perry and Stubbs (1978)); Telomerina flavipes (Meigen, 1830) (regarded as a predominantly necrophagous species but develops also in various excements and found also in burrows of small mammals and birds (Rohácek 1983)); Phyllomyza longipalpis (Schmitz, 1924) (an extremely rare species found now in high numbers); Desmometopa sordida (Fallén, 1820) (numerous records from rotting vegetable material and dung, inch my own data (Papp 1992); Fannia aequilineata Ringdahl, 1945 (known to breed in dung, in nests of birds (Lyneborg 1970) but also from tree holes with rotting wood (Skidmore 1973)). Lycoriella cellaris (Lengersdorf, 1934) has not been recorded from wasp's nests either. Buck et al. (1997) reared numerous specimens from beef baits, other records are from cellars and on rotting vegetable material; they regard this species as "eurytopic saprophage" together with the other necrophagous sciarids they found in their rearing experiments. Buck et al. (1997) think the larvae probably feed on fungal mycelia. This species is new for the Hungarian fauna. Fannia scalaris (Fabricius, 1794) larvae are very polyphagous (see Ferrar 1987: Table 34.1). Potamia littoralis Robineau-Desvoidy, 1830 is one of the commonest forest species breeding in birds nests in hollows (e.g. Skidmore 1965) - reared from them several times also by me -, but known also from nests of social Hymenoptera (Ferrar 1987: Table 51.2). Unfortunately, no comparison can be made for the Cecidomyiidae species and for the Megaselia species, since they were not actually identified. To sum it up, one can say that an extremely high number of flies of medium diversity (19 spp.) were reared from the two hornet's nests. Four litres of hollow medium produced 1295 dipterous specimens, while 9-10 litres in the other nest was a medium for 6930 flies. These data may contribute to a more realistic image of the abundance of the forest flies. Nests of social Hymenoptera are among those small-sized feeding sources, which maintain a high diversity of forest flies, although the forest plants and litter themselves are media for a limited number of species.