Potential Impact of Metarhizium anisopliae on the Diamondback Moth (Lepidoptera: Plutellidae) and Its Parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae). Laboratory studies were conducted to evaluate the effect of the Metarhizium anisopliae against the diamondback moth, Plutella xylostella and its parasitoid, Diadegma semiclausum. A completely randomized design consisted of 5 treatments (4 concentrations of conidial suspension: 5 x 104, 3.5 x 105, 2.5 x 106, 1.2 x 107 conidia/ml and control) was used. The results indicated that the mortality of P. xylostella larvae were significantly induced by the fungal treatments. A significant reduction in pupation and adult emergence of P. xylostella was also detected in all treatments when compared with that in the control. The fungus might also result in a male-biased sex ratio of the surviving P. xylostella. When applied at a concentration of 1.2 x 107 conidia/ml, M. anisopliae might significantly reduce the survival of the parasitoid, D. semiclausum. Thus, despite its potential as a biological control agent against P. xylostella, the entomomogenous fungus M. anisopliae was also detrimental to the larvae parasitoid D. semiclausum.