The insect pathogenic hyphomycete fungus Metarhizium anisopliae (Metschnikoff) Sorokin is promising as a biological insecticide for many species of subterranean termites. In Australia, a survey of termite mounds and feeding sites using a selective medium showed that this fungus is widespread but rarely causes mortality of termites under natural conditions. One isolate, codenamed FI610, has been selected for detailed field trials on the basis of its high virulence for a range of termite species and efficacy at high temperatures. Various options for using this fungus as a biological insecticide are now being evaluated in the field. These include: (1) Direct treatment of termite nests. As little as one gram of pure conidia may suffice for control depending on correct application of the formulation and the time of year in which it is carried out. Spores persist for at least two years in the nest; (2) Spraying directly onto and/or into timber structures to protect at least for a certain period against termite damage, relying on the repellency of the conidia to Australian species of termite; (3) Mixing of conidia into soil to create a barrier around timber structures. Depending on circumstances over two years protection of timber has been achieved in SE Australia; (4) Use of the fungus as the controlling agent in bait systems. The major factor limiting the efficacy of Metarhizium anisopliae especially in baiting systems is the behavioural response of healthy termites to the applied fungal conidia, to foraging termites carrying conidia and to termites infected with the disease.

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