LOCATION OF IMMATURE STAGES OF THE MUSHROOM INSECT PEST MEGASELIA-HALTERATA IN MUSHROOM-GROWING MEDIUM

Experiments were conducted to examine the location of oviposition by t he phorid fly Megaselia halterata (Wood) (Diptera: Phoridae) in uncase d and cased compost. Clearly, a majority of the gravid females choose oviposition sites directly after entering the top layer of the compost . In uncased compost, 60% of all adults emerged from the top of four c ompost layers of equal thickness. When the compost was covered by a ca sing layer which was still uncolonized by Agaricus bisporus, ovipositi on was further concentrated in the top compost layer. In this situatio n, 91% of all adults emerged from the top compost layer whereas only 1 .5% emerged from the casing. When the casing layer was colonized by mu shroom mycelium, 45% of all adults emerged from the casing layer and 5 3% emerged from the top compost layer. Further concentration in the to p compost layer and the casing layer occurred as a result of upward mi gration of larvae. When compost was cased after oviposition, up to 43% of all adults emerged from the casing layer. We concluded that in the control of phorid infestations with insect pathogenic nematodes, appl ications in uncased compost can be restricted to the upper compost lay er. When compost and casing are filled simultaneously, nematode applic ations in the casing layer only could be considered.