Risk assessment of an exotic biocontrol agent: Phytoseiulus persimilis (Acari : Phytoseiidae) does not establish in rainforest in southeast Queensland

The Chilean predatory mite, Phytoseiulus persimilis Athias-Henriot, appeare d in Australia in 1978 soon after being introduced into New Zealand as a sp ecialized biological control agent of spider mites. It is known to be natur alized in agricultural habitats in southeast Queensland, Australia, althoug h nothing is known about its distribution in native ecosystems. In order to determine whether P. persimilis is able to invade subtropical rainforest, we placed potted bean plants infested with its preferred prey, the two-spot ted mite (Tetranychus urticae C.L. Koch), at 50 m intervals for 200 m on ei ther side of the rainforest-field ecotone at four sites in southeast Queens land. Two, 4 and 6 weeks after placement, five leaves were sampled from eac h pot and any phytoseiid mites present were identified. The initial experim ent took place in the spring and was repeated in summer and in autumn of 19 97. At all four sites and in all three seasons I! persimilis rapidly coloni zed all of the pots in fields. In the rainforest, however, some pots were n ever colonized and significant populations of the predator developed only i n the summer, and then only at the first stations, 50 m into the forest. Th ese results suggest that even when its preferred prey is present, subtropic al rainforest is not an appropriate habitat for P. persimilis. In addition, we reviewed extensive collections of phytoseiid mites from native forests and synanthropic habitats in Australia and found P. persimilis records only from fields, glasshouses, gardens, weeds, roadsides and similar disturbed habitats dominated by introduced plants, again suggesting that this biocont rol agent is not a rainforest invader.