Paul D. Pratt, Brian A. Croft and Jack DeAngelis
Department of Entomology, Oregon State University
Cordley Hall, Corvallis OR 97331
Office: (541) 737-4733 Fax: (541) 737-3643
Introduction
Spider mites are major pests of commercial ornamentals. These mites, specifically the two spotted spider mite (Tetranychus urticae Koch), are among the most injurious pests in the USA and are ubiquitous in nurseries worldwide. Spider mites typically feed on plant foliage, resulting in abnormal growth, chlorosis, reduction in photosynthesis and defoliation. Because of their high reproductive potential and short generation time, spider mites can rapidly increase to damaging levels on susceptible plants.
Historically, ornamental producers have relied on chemical pesticides to suppress spider mites. These pesticides are often only marginally effective against mites but may decimate sensitive natural enemies, specifically predatory mites. Similarly, broad-spectrum insecticides directed at other pests (i.e. aphid, root weevil, etc.) may negatively affect predatory mites and result in secondary or induced outbreaks of spider mites. Resistance to pesticides also is common among spider mites and fewer pesticides for ornamental production are registered each year.
An alternative to the use of pesticides for spider mite control is the inoculative release of predatory mites into nurseries. Recent studies evaluated the predator Phytoseiulus persimilis for suppression of the two spotted spider mite (T. urticae) in outdoor ornamentals grown in semi-tropical regions of the USA. Results suggest that the predatory mite can reduce the two spotted spider mite on ornamentals, with the potential of eliminating miticide applications. Unfortunately, P. persimilis is not an ideal biological control candidate for all ornamental growing regions due to climatic incompatibility and tendencies to provide only short-term control. Also, earlier studies that focused on biological control of the two spotted spider mite but have ignored other important mite pests of ornamentals such as the southern red mite (Oligonychus illicis McGregor), the spruce spider mite (Oligonychus ununguis Jacobi), the citrus red mite (Panonychus citri McGregor), the bamboo mite (Schizotetranychus celarius Banks), the European red mite (Panonychus ulmi) and various tarsonemid, and eriophyid mites.
Therefore, the goal our research was to identify and evaluate a predatory mite biological control agent of multiple spider mites that could ultimately be incorporated into an integrated pest management (IPM) program for ornamental nurseries in western regions of the Pacific Northwest, USA. To do this we had the following objectives:
