Mite vs. Mite
(This column was first published in the April 5, 1999 Buffalo News.)
We are blessed here on the Niagara Frontier with our fine orchards and vineyards. Even as I write, my mouth waters for a bunch of our Concord grapes, a Gala apple or a Red Haven peach. So my heart goes out to our fruit growing neighbors who so carefully tend these groves. They certainly have their troubles. If it isn't a late freeze that ruins their buds or a hailstorm that destroys their crop, it is an Alar scare* that turns people away from their products. And there are always the omnipresent "bugs."
One enemy in particular, European red mites (abbreviated ERMs by pest controllers), are posing serious problems for orchardists and vinyardists. Mites, like spiders, have eight legs but, together with ticks, they belong to a separate order in the arthropod phylum. This red mite has always been widely distributed in Europe and it has spread rapidly since it was first identified in this country in 1911.
ERMs are so small they are almost invisible to the naked eye. Full grown they measure less than a 25th of an inch. They feed by piercing individual leaf cells and sucking out the contents including life-sustaining chlorophyll. As individuals they do little damage. Even a half dozen per leaf does not usually represent a problem and that is a great many mites -- about 50,000 on an average fruit tree. But many more than that and matters get serious. Leaves turn bronze and drop off and plant production shuts down.
Until recently these ERMs have been controlled by pesticide spraying but, as so often happens, the mites are developing resistance to the sprays while the chemicals continue to kill their beneficial predators. This bodes ill for future outbreaks.
But here is where the story gets interesting. It turns out that there is little loyalty in the mite world. Two of the most serious predators on European red mites are other mite species. A Canadian entomologist, Phil Lester of Queen's University and Agriculture Canada in Vineland, Ontario, is breeding pesticide tolerant predatory mites. He builds up this tolerance by exposing generations of the predatory mites to pesticides until the few remaining form a strain that can handle the poisons. This mirrors the more prolific ERMs' path to immunity.
Now the predatory mites are reintroduced to prey on their "cousins." Unfortunately this sounds far easier than it is to carry out this process in the orchard or vineyard. Jan Nyrop, a Cornell University entomologist, has worked out several alternate plans for this project. First, the predatory mites have to be identified in a source orchard or vineyard. Then the twigs, flowers or leaves on which they are found are carried to the target trees or vines and attached there. (The timing and procedures differ for the three carriers.) This is, of course, a labor intensive and therefore costly process, but it represents an investment which will realize future savings in pesticide costs.
After a fruit grove is inoculated with predatory mites it takes two to three years for them to multiply to the level at which the ERMs are controlled. But after that time the grower no longer needs to apply any miticides. The ERMs are not completely killed off but their populations are brought into balance with those of their predators and the orchards become self-maintaining -- at least as far as mites are concerned.
I salute the entomologists for their endeavors and for the assistance they are providing to our beleaguered fruit growers. Of course, I admit to selfishness here as well. The more apples, peaches and grapes the better as far as I am concerned. -- Gerry Rising