TSM for two: Combined use of Feltiella acarisuga Vallot (Diptera: Cecidomyiidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) for biological control of Tetranychus urticae Koch (Acari: Tetranychidae) on greenhouse tomatoes

Experimental methods and theoretical approaches were employed to assess the prospect for use of the two predators, Phytoseiulus persimilis Athias-Henriot and Feltiella acarisuga Vallot in combination to control infestations of the two-spotted spider mite, Tetranychus urticae Koch, on greenhouse tomatoes. Laboratory and field experiments were designed to determine whether the predators' efficacy was affected by close proximity to the other predator. Results showed no detrimental effect on the total combined consumption of T. urticae over a 24-hour period in enclosed arenas with different proportions of the two predators added. A deterministic model was developed to calculate the amount of damage by T. urticae on greenhouse tomatoes over 6 weeks of an infestation. The model calculated the effects of additions of the two predators of spider mites on the size of an existing population of spider mites. Results of this analysis have implications for use of combined predation in greenhouse biological control. Timing of release and immigration and emigration of all three arthropod species and predator survivorship are factors that could be manipulated to achieve improved biological control of two-spotted spider mites.