IMPROVED CONTROL CAPACITY OF THE MITE PREDATOR PHYTOSEIULUS-PERSIMILIS (ACARI, PHYTOSEIIDAE) ON TOMATO

The predatory mite Phytoseiulus persimilis is frequently reported to p erform poorly on greenhouse tomatoes. As the predators are mass-reared on another host plant (bean), we supposed that they are poorly adapte d to tomato, a plant densely packed with poisonous and sticky glandula r hairs. This hypothesis was tested by comparing the control capacity of a strain of P. persimilis directly obtained from a mass rearing wit h the same strain after four generations on tomato. Both strains were released in a tomato crop in two identical compartments of a greenhous e and the population dynamics of prey (a tomato strain of Tetranychus urticae) and predator were recorded at weekly time intervals. It was f ound that the strain previously exposed to a tomato environment perfor med better than the unexposed strain: (1) its population increased fas ter; (2) the prey population declined faster; and (3) the damage to ne w-grown tomato leaves was considerably lower. To investigate the cause s of the difference in performance between the exposed and unexposed s trains, oviposition and survival rates were assessed on a diet of twos potted spider mites on tomato leaf sections. In addition, the unexpose d strain was tested on a diet of two-spotted spider mites on bean leaf sections. The difference in oviposition rates of both predator strain s was small compared to the overall mean. However, the oviposition rat e of the fist generation of predators since transfer from bean to toma to dropped to less than half of the original value. Moreover, mortalit y in the first generation increased from 14% to 89%, whereas it decrea sed to 0% after four generations. Future research should clarify wheth er these changes in life history are due to selection or to physiologi cal adaptation.