Influences of the Method of Introduction of Prey (tetranychus-urticae) and Predators (phytoseiulus-persimilis) On the Development of Plant Injury in Tomato Crops Under Glass

Two variants of the ''pest in first'' method of introduction of prey (Tetranychus urticae Koch) and predators (Phytoseiulus persimilis Athias-Henriot) on tomato crops were compared in a 80 M2 glasshouse. As opposed to the second crop, the first crop was protected against spider mites by early and multiple releases of predators ensuring high spatial coincidence between prey and predators. Plant injury gradually increased in crop 1, whereas it first peaked and then decreased to low values in crop 2. Mean plant injury was higher in the former crop, and so was the degree of spatial variability. The lack of persistent control in crop 1 indicates that the predators suppressed, but did not annihilate the spider mites in the prey patches where the predators were introduced. This enabled the spider mites to resurge shortly after their enemies had disappeared due to lack of food. In crop 2, the way the biological control was conducted permitted the predators to achieve so high densities that they could annihilate the spider mites in most patches. Not only did this synchronize the prey populations but it also prevented the pest from a fast recovery. Moreover, predators did not disappear and maintained spider mite populations at low levels.