Maintenance of predatory phytoseiid mites for preventive control of strawberry tarsonemid mite Phytonemus pallidus in strawberry plant propagation

Effective means for the control of the strawberry tarsonemid mite, Phytonemus pallidus, are needed for organic strawberry plant production. To study the effect of predatory mites as a preventive control tool of P. pallidus, four species of predatory mites were released on mite-free strawberry plants in a greenhouse experiment. Phytoseiid mites were fed by scattering cattail pollen on leaves until the artificial infestation of the strawberry tarsonemid mite took place 6 weeks later. Population dynamics of predatory and phytophagous mites and thrips were monitored every second week by sampling leaves, runners and whole plants. The predatory mite species Anthoseius rhenanus, Euseius finlandicus and Neoseiulus cucumeris successfully reproduced and remained on plants when fed with pollen, whereas Neoseiulus barkeri failed to reproduce before the introduction of P. pallidus. After the artificial infestation of P. pallidus and the termination of pollen feeding, A. rhenanus, N. cucumeris and N. barkeri were able to control the build-up of tarsonemid mite populations for a period of 3 months. A. rhenanus and N. cucumeris were found to be the most promising preventive predators against P. pallidus. At the end of the study N. cucumeris and N. barkeri replaced E. finlandicus and A. rhenanus, and were able to form mixed populations when prey mites were richly available. However, the phytoseiid mite species used in this study could not prevent the development of the natural infestation of the two-spotted spider mite, Tetranychus urticae, after the initial study was terminated.