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 mi te Tetranychus urticae Koch in the ornamental crop gerbera with the use of the predatory mite Phytoseiulus persimilis Athias-Henriot for biological co ntrol. We used four gerbera cultivars on which the intrinsic rate of popula tion increase (r(m)) of Il 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 r(m) 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 t o the population growth rate, we discarded the first egg of all predators f rom our analyses. The egg-to-second-egg developmental time of the predator was approximately 5.2 days. This developmental time was slightly but signif icantly shorter on gerbera cultivar Fame than on the other three cultivars. However, this shorter developmental time did not lead to a higher r(m) of the predators on this cultivar. No cultivar effect was found on the peak ov iposition rate, which varied from 5.1 to 5.4 eggs/female/day. On the cultiv ars used, the r(m) 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 r(m) of the predators, which ranged from 0.43 to 0.45 per d ay. Hence, the capacity for population increase of P. persimilis is not inf luenced by host plant resistance to its prey. (C) 1999 Academic Press.