WHAT CAUSES SPIDER-MITES TO GO DORMANT?

Spider-mites are some of the most prevalent pests wherever gardeners garden, and they have this sneaky habit of showing back up when you think they're long gone. Sometimes that's just because spider mites are present almost everywhere in the world, and they happily float along on wind currents, crawl, or "hitch-hike" to find new plants to colonize, so they do seem to spread themselves around about everywhere. Come fall and winter, though, they have another tricky feature for surviving dormant through the long winter called "diapause". Under natural outdoor lighting and temperature conditions, in the fall spider-mites "sense" that winter is approaching , and begin undergoing several physiological changes. Adult female spider-mites discontinue feeding, mating, and other normal spider-mite activities, and turn almost completely red in color (as opposed to their normal, semitransparent green color with two black spots, one on each shoulder). The two spots become almost invisible beneath the solid red color. (Body shape becomes the main way to differentiate them from reddish-colored predatory mites at this time.) After these changes occur, spider-mites begin migrating to hiding spots, to survive the winter. Outdoors, these hiding spots might be in a crevice in a tree trunk, or similar protected places. (In cool greenhouses, they'll hide in any crack or crevice available.) They don't become active again until spring, when new foliage begins growing and daylength increases. If you didn't know better, you'd swear they just "showed up" from out of nowhere!

Over eons of time, spider-mites have learned to go dormant when the length of hours of daylight start getting lower, seemingly aware that cold temperatures will soon follow. Other factors enter into it, such as temperature, but photo-period appears to be the main cause. The specific amount of hours of daylight required to bring on dormancy varies according to latitude (farther north, where it gets cold early, they go dormant sooner), but it's somewhere in the neighborhood of 13 hours a day of light everywhere. They don't all go into diapause at that same exact time, either, as individual spider-mites have quite a variance in their response to these stimulations. This ensures that if there's an early winter some will already be in hiding, and if it's a normal or late winter, some die-hard spider-mites are still there munching on plants as long as possible, but generally, they tend to go dormant at daylengths lower than about 13 hours a day. It's a system that's worked real well for spider-mite survival, and virtually guarantees that spider-mites will be a continuing problem for gardeners. Come spring, when the number of hours of daylight increases above their trigger-threshold, they come back out, turn normal color, and resume all normal spider-mite activities, ready for a new season of eating plants.

Unfortunately for indoor gardeners, spider-mites don't necessarily go through this same cycle when they're inside heated indoor and greenhouse environments, so a wintertime reprieve from their damage can't be counted on. That's because, just as cold temperatures help spider-mites go into dormancy, warm temperatures can prevent it, so they can continue staying active all year round irregardless of daylight length. In fact, nature has built in so much adaptability in spider-mites that they just seem to "know" when conditions will be suitable for their success, and they usually seem to show up, often just about the same time every year. Although the cooler temperatures of wintertime slows down spider mite breeding (they don't seem to actually stop breeding unless it's cooler than about 52F), spider-mites can and do remain as an indoor pest all year long. For these reasons gardeners need to be ever-vigilant for the presence of spider-mites, because they seem to be a near-universal plague for gardeners.

Spider Mite Predators are your best long-term control, so at the first sign of pest mites, apply Spider Mite Predators for control. For more advanced cases or faster control, use Spider Mite Destroyers or try other, more general-purpose controls.

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