Abstract

To select a biological control agent for suppression of spider mites on landscape plants in western regions of the Pacific Northwest, we compared life history traits of Galendromus occidentalis Nesbitt, Neoseiulus californicus (McGregor) and Neoseiulus fallacis (Garman). We also evaluated abilities of these predatory mites to suppress spider mites in 4 landscape plant species under field conditions. Comparing life history traits from the literature, intrinsic rate of increase was similar between the 2 Neoseiulus species but lower for G. occidentalis. Prey killed per day was greatest for G. occidentalis > N. fallacis > N. californicus. For overwintering abilities, N. fallacis and G. occidentalis are indigenous to the Pacific Northwest and will survive winter assuming overwintering sites are available, but survival of N. californicus is unlikely. Neoseiulus californicus has the widest prey range, G. occidentalis the narrowest, with N. fallacis intermediate. When inoculated into spider mite infested landscape plants, N. fallacis was equally effective at suppressing spider mites as G. occidentalis in either Malus rootstock or Acer shade trees. Further tests with N. fallacis or N. californicus on Spiraea and Rhododendron plants suggested that N. fallacis is equally or more effective at suppressing pest mites, respectively. Compared with the other candidates, N. fallacis was equally effective at controlling pest mites and has a wider prey range than G. occidentalis. Neoseiulus fallacis appears to be the best candidate for biological control of multiple spider mite species on landscape plants in these parts of the Pacific Northwest.