Compatibility of Host Plant Resistance and Biological Control of the Two-Spotted Spider Mite Tetranychus urticae in the Ornamental Crop Gerbera

We investigated the compatibility of host plant resistance to the spider mite Tetranychus urticae Koch in the ornamental crop gerbera with the use of the predatory mite Phytoseiulus persimilis Athias-Henriot for biological controL We used four gerbera cultivars on which the intrinsic rate of population increase (rm) of T. urticae was previously found to differ largely. We performed life-history studies on those cultivars with P. persimilis and determined whether the developmental time, peak oviposition rate, and (rm)of the predator was influenced by host plant resistance. Because the first egg of P. persimilis is usually a male and therefore does not contribute to the population growth rate, we discarded the first egg of all predators from our analyses. The egg-to-second-egg developmental time of the predator was approximately 5.2 days. This developmental time was slightly but significantly shorter on gerbera cultivar Fame than on the other three cultivars. However, this shorter developmental time did not lead to a higher(rm) of the predators on this cultivar. No cultivar effect was found on the peak oviposition rate, which varied from 5.1 to 5.4 eggs/female/day. On the cultivars used, the (rm) of the spider mites was previously found to vary from 0.09 to 0.23 per day. We did not find any effect of spider mite resistance in gerbera on the (rm) of the predators, which ranged from 0,43 to 0,45 per day. Hence, the capacity for population increase of P. persimilis is not influenced by host plant resistance to its prey.