University of Maryland Extension

Biological Control of Spider Mites

Two predaceous mites, Neoseiulus californicus and Mesoseiulus longipes, tolerate low humidity levels and high temperatures and can be used in interiorscape situations as well as in production greenhouses. N. californicus tolerates the highest temperatures of the available predaceous mites. It is a slow acting (long lasting) mite. These two predaceous mites are also sold for spider mite control as a combination so releases do not need to be made each week. The recommendation is to release again after 2 – 6 weeks or when necessary. Monitor plants for the presence of predaceous mites (look for mites with long legs that are fast moving). Predaceous mite eggs are 3 – 4 times larger than pest mites and are long, not round. Reapply predators if there are more than 30 pest mites to one beneficial mite. Washing plants in interiorscapes often wipes out the predator population. Both species reproduce in interiorscapes. The predaceous mite, Phytoseiulus persimilis, does not reproduce in interiorscapes because the environment is too dry.

Factors To Consider Before Releasing Beneficial Organisms

• Identify the pest in order to choose the correct beneficial for control.

• Avoid pesticides that are toxic to the beneficials (it might be necessary to knock down the pest population to increase the effectiveness of the beneficals which do not reproduce as quickly as the pests).

• Know when the beneficials will arrive and be ready to release them immediately.

• Check the viability of the shipment.

• Beneficial nematodes are the only beneficial organism that requires refrigeration. For the others, check the shipping package for the temperature. If warm, predator survival could be low. Predators can be stored at about 50 °F (which is the temperature in packaging with a cold ice pack).

• It is best not to hold overnight if at all possible. Do not hold over the weekend before releasing.


February 2013
Source: Integrated Pest Management Program for Commercial Ornamental Horticulture, University of Maryland Extension, CMREC, Ellicott City, MD
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