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!
HOW DO SPIDER MITES "SENSE" WHEN TO GO DORMANT?
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
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 52¡), 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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