Parasitus bituberosus (Acari: Parasitidae), a possible agent for biological control ofHeteropeza pygmaea (Diptera: Cecidomyiidae) in mushroom compost

The prey items accepted byParasitus bituberosus Karg included all immature instars ofHeteropeza pygmaea Winnertz, first and second instars ofLycoriella solani together with its eggs, and compost nematodes and springtails. A preference was shown by deutonymphs for first-instarH. pygmaea, whereasHistiostoma feroniarum andPygmephorus sp. were not accepted. Adult mites, especially females, appeared to be even more voracious predators on first-instarH. pygmaea than were deutonymphs or protonymphs. The mite preventedH. pygmaea from reaching high populations in both laboratory-scale and small commercial-scale compost units; it also reduced populations of free-living nematodes in the latter. The distributions ofH. pygmaea and the mite throughout the compost in growing-bags were investigated and found to parallel each other. The mite was able to penetrate all parts of the compost. There was no evidence that it damagedAgaricus bisporus, and it was never found on harvested caps.