An important and interesting aspect of biological control program is to use multiple biocontrol agents simultaneously. Metarhizium anisopliae is one of the most common entomopathogenic fungus against flies, including sciarid flies. The predatory mite Gaeolaelaps aculeifer (= Hypoaspis aculeifer) (Acari: Laelapidae) has been commercially available as a biological control agent against soil-born pests including eggs and larvae of sciarid flies. Refering to pesticide problems such as evolution of resistance in the sciarid flies in button mushrooms productions, this study investigated the outcome of individual efficiency and interactions between the entomopathogen M. anisopliae with the predatory mite G. aculeifer, as well as their effect on the control of the L. auripila. Experiments were carried out under laboratory conditions at 23±1 °C, 60 ± 5% R.H. and photoperiod of 0: 24 (L: D) h. The conidia of M. anisopliae was sprayed on experimental containers (7 ×4 cm) that their foam were covered with a mixture of plaster of Paris and charcoal (ratio 7 : 1) on mushroom compost in different concentrations including 103 to 108 spores/milliliter individually or in combination with one G. aculeifer. The experiment was replicated 15 times, each replicate with 15 of second instar of fungus gnats. Results showed that females of G. aculeifer consumed 4.41 ± 0.26, 2nd instar larvae of L. auripila in 24h. Also, the mortality rate of this pest was 89.14 ± 2.19% in combined treatment (G. aculeifer + 108 spores/milliliter M. anisopliae). The mortality rate of L. auripila in single application of entomopathogenic fungus M. anisopliae at different concentrations from 103- 108 spores/milliliter was 1.69 ± 0.26 to 12.82 ± 0.36 % while in combination treatment was 8.01 ± 0.51 and 13.37 ± 0.33, respectively. In conclusion, in most cases the interaction of G. aculeifer and M. anisopliae imposed the highest mortality to L. auripila population. Our study suggests that application of M. anisoplia
