Article 1-6 Persimilisa Predator Against Spider Mites

A biological control agent effective against spider mites is available from a Vancouver Island company, Nature’s Alternative Insectary, Ltd. (NAI). Spider mites are common pests and can be identified as small spider-like mites, visible on plants as black dots on the leaves, with a close-up view showing dark lateral spots on the abdomen. They are usually found on the underside of the leaves and cause bleached areas on plants. Advanced stages of infestation show webbing on leaves, bud drop and withering of the dried out plants, with eventual plant death. All life stages of this pest feed on plants via a piercing and sucking action and their dispersal can be very rapid as they use webbing, air currents and getting carried by plant caretakers to spread throughout the crop. Care should be taken when days begin to shorten as spider mites can hibernate over winter. For this reason, a thorough clean up should be done to help prevent re-infestation the following spring. Spider mites are resistant to many chemicals, therefore control using a biological can be much more effective. Combating spider mites is possible with the help of a natural enemy, the spider mite predator Phytoseiulus persimilis, commonly called Persimilis.

Persimilis was one of the first biological control agents developed and is a voracious spider mite predator for use in greenhouses, on indoor plantscapes, on houseplants and in some field crops. Both nymph and adult stages of Persimilis feed on all stages (egg, nymph, and adult) of spider mites and this predator can eat 5 to 20 mites per day. Persimilis is able to control spider mites in a crop because the Persimilis life cycle occurs about two times faster than that of the pest. The predators are active searchers who do not produce webbing but have long legs, and are able to move through the crop rapidly to feed. Dispersal of the predators is improved if the leaves of the plants touch each other. Persimilis should be applied at the first signs of spider mite presence therefore thorough visual monitoring of plants is necessary. The predators are capable of eating all spider mites in a crop by sucking them dry, after which point the Persimilis will die off. For this reason, reapplication of the predator is necessary if another infestation occurs. Also, multiple applications of the predator may be necessary to maintain pest control. Successful control of the mites is evident when plants outgrow any damage symptoms.

Persimilis is available in different forms for release. At Nature’s Alternative Insectary a container of granular material is used as a carrier, which when opened releases the orange-red, 0.5mm predators. This material containing the Persimilis can be sprinkled at the base of crop plants as the predators will run up the plants. Persimilis is also available on leaves. This method for release has the advantage of introducing all life stages, including oval eggs, pale salmon-colored immatures, and orange-red adult predators into a crop. This allows an even population to be distributed on the plants. These leaves are placed on infested leaves in a crop and, when left for 48 hours, allow the Persimilis eggs to hatch. The dried up pieces of leaf can then be removed for aesthetic purposes but will cause no harm if left on the plants. After introduction Persimilis will establish itself in a mite-containing crop under proper conditions. Controlling environmental conditions will favor optimum performance of Persimilis for spider mite control. Temperatures of 20° to 27°C favor Persimilis, while temperatures higher than this favor more rapid reproduction of the pest. It is also helpful to maintain a relative humidity higher than 60%, as this increases Persimilis reproduction whereas spider mites prefer dry conditions. One easy way of favoring this condition is by misting the plants or by using a household cool-mist humidifier.

Other practical information recommended by Nature’s Alternative Insectary is important when applying spider mite predators. Containers of predators should be stored in a cool dark place, especially out of direct sunlight, until they are to be used. Also, the Persimilis should be released as soon as possible after receiving the biological, preferably on the day of receipt. Introduction rates vary with the level of infestation of spider mite. Close monitoring should enable a grower to catch infestations early, however a heavier pest problem will require more predators to be used. If combining biological and chemical control mechanisms in an Integrated Pest Management system it is important to know which chemicals are compatible with Persimilis. Persimilis is a very effective biological control method for spider mites. Use of Persimilis is beneficial to both small and large-scale growers. Organic growers should be particularly interested in using these predators, as their use is ecologically sound and effective.