PERSISTENCE AND CONTAINMENT OF METASEIULUS-OCCIDENTALIS (ACARI, PHYTOSEIIDAE) IN FLORIDA - RISK ASSESSMENT FOR POSSIBLE RELEASES OF TRANSGENIC STRAINS

Metaseiulus occidentalis (Nesbitt) is a phytoseiid mite which is comme rcially available as a biological control agent of spider mites. Genet ic manipulation of this phytoseiid species has yielded transgenic stra ins. but none have been released into the environment. Previous data s uggested that M. occidentalis could not survive the wet, humid summers in Florida. A non-transgenic strain of M. occidentalis was released i nto field plots in Gainesville on soybean plants infested with the two -spotted spider mite, Tetranychus urticae Koch. Populations were monit ored from April-October 1994, and weather data were gathered at the re lease site. Permethrin-treated barrier rows were monitored to determin e if the mites dispersed outside the plots, and aerial dispersal was m onitored with sticky traps. Predator and spider-mite populations repea tedly crashed during the summer months, and population growth was nega tively correlated with rainfall. CLIMEX, a population growth model whi ch uses climatic factors to determine whether a given poikilothermic s pecies can colonize and persist in new geographic areas, also indicate d that M. occidentalis cannot persist through the wet season in Florid a, although it may be able to establish and persist through the fall, winter and spring months.