For many years, California strawberry growers have released predatory mites for biological control of spider mites. One of the preferred species for this use, which is commercially available, is Phytoseiulus persimilis. Research in Canada indicates that this predator may also be effective for controlling twospotted spider mite in raspberry.
The research was conducted in 1989 on red raspberries at the Agriculture Canada Research Station at Agassiz, British Columbia. The plants were artificially infested with twospotted spider mites in July, and the predator releases were conducted in early August when there was an average density of 0.7 twospotted spider mites per leaflet. In addition to an untreated control, there were three experimental treatments, each representing a single release of different levels of the predatory mite. The specific release rates were based on the ratio of predators released to adult female spider mites present; the ratios were 1:50 (high rate), 1:100 (medium), and 1:200 (low). Counts of both pest and predator mites were taken weekly for eight weeks following release of the predators.
The predator mites established and increased approximately ten-fold within 3½ weeks of release. By this time, the twospotted spider mite populations were declining relative to the untreated controls. Declines were most evident at the high and medium release rates. The populations of pest mites were statistically significantly lower at the high and medium release rates at 4½ weeks after predator release. The researchers concluded that, under their conditions and similar situations, P. persimilis may be able to reduce spider mite populations on raspberry.
P. persimilis is available from many of the North American suppliers of biological control agents.
Wood, L., D. A. Raworth, and M. Mackauer. 1994. Biological control of the two-spotted spider mite in raspberries with the predator mite, Phytoseiulus persimilis. J. Entomol. Soc. Brit. Columbia 91:59-61.
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