Gerbera jamesonli is an ornamental crop of which a large number of cultivars is grown commercially. Previous research by our group has revealed large differences between these cultivars in suitability for population increase of the spider mite Tetranychus urticae. This paper adresses the question whether cultivars that differ in suitability for spider mites are equally suitable for the predatory mite Phytoseialus persimilis, which is the main predator of T. urticae. Life-history studies were performed with P. persimilis to determine the intrinsic rate of population increase, rm, on three gerbera cultivars that differed largely in resistance to F. urticae. The rm was nearly identical on the three cultivars, varying from 0.41 to 0.43 per day.
All cultivars produce a large number of volatiles in reaction to spider mite damage.
Many of these volatiles are produced in very large quantities. The volatile blends do not differ qualitatively among cultivars and the blends of all cultivars tested are attractive for the predatory mite P. persimilis. All cultivars produce three terpenoids and a phenolic compound which previously have been shown to attract predatory mites when they are offered individually to the predators. The gerbera cultivars also differ in the production of a number of other terpenoid compounds and some phenolic compounds. In conclusion, our data show that the population growth rate of the predatory mites is not influenced by host-plant resistance to spider mites.