WINTER ABUNDANCE OF SOIL DIPTERA LARVAE IN ARABLE SOIL

In the winter seasons 1990-91 and 1991-92 the abundance of soil Dipter a larvae in arable soil in two Danish cereal fields was studied. Cecid omyiidae, Chironomidae and Sciaridae contributed 84 - 92% of all dipte ran larvae and 85% of adult soil Diptera emerging from the fields in A pril-June. Cecidomyiidae were predominant soil Diptera and the taxonom ic composition of cecidomyiids recorded is presented. Free-living larv ae of Lestremiinae were predominant, but pest species of Cecidomyiinae , viz. Dasineura brassicae Winn. and Sitodiplosis mosellana (Gehin) as sociated with previous and actual crop respectively, were also abundan t. In species of Monardia (Cecidomyiidae, Lestremiinae) paedogenetic l arvae occurred. During the winter season soil Diptera larvae were reco rded in densities of 400 - 1200 m-2, which are comparable to density e stimates of adult Diptera hatching from the fields in April June. Larv al densities of Cecidomyiidae, Chironomidae, Sciaridae and Empididae a re presented. Compared with abundance of soil Diptera larvae published from arable fields. temperate grassland and woodland, the larval dens ities found are at the lower end of the range recorded. The density of larvae of Lestremiinae was significantly reduced after autumnal ploug hing. The abundance of trophic groups of soil Diptera larvae in arable fields and woodland is compared.