BIOLOGICAL CONTROL Seasonal Abundance of Spider Mites and Their Predators on Red Raspberry in Quebec, Canada

Seasonal abundance of spider mites and their predators on red raspberry was studied in 1993 and 1994 at 2 agricultural locations near Quebec City, Canada. Three raspberry systems, wild raspberry, pesticide-free cultivated raspberry, and commercial raspberry treated with a variety of pesticides, were sampled at frequent intervals. Tetranychus mcdanieli McGregor accounted for 87.5, 80.6, and 95.0% of the identiÞed spider mites collected in the commercial, untreated, and wild systems, respectively. Tetranychus urticae Koch was observed in low numbers in both years. Spider mites were more abundant in the commercial and untreated systems than in the wild system, and there was generally no difference between commercial and untreated systems in 1993, whereas in 1994 there was more spider mites in the commercial system than in the untreated one. Predatory mites were present in all systems. Amblyseius fallacis (Garman) was the most abundant predator in the commercial system, whereas a complex of other predatory mites species dominated the wild system. The coccinellid Stethorus punctillum Weise was abundant in the untreated system and rare in the commercial and the wild systems. Variations of predator abundance among treatments did not correlatewithvariationsof spidermite abundance, andcouldbeexplainedby seasonal predator-prey asynchrony.