Margaret Lauterbach: Destructive spotted wing drosophila found in southern Idaho

Idaho has been recently invaded by a destructive insect — spotted wing drosophila, a type of vinegar fly that seeks out growing, ripening fruit in which to lay eggs. Vinegar flies, another species of drosophila, favor fermenting or rotting fruit, but they’re no threat to commerce. Spotted wing drosophila is a commercial threat.

These flies were present in southern Idaho in low numbers until near the end of summer, according to Jim Barbour, entomologist and superintendent of the Parma Research and Extension Center of the University of Idaho.

This tiny, spotted-wing fly is significantly more destructive than vinegar or fruit flies, because it can and does lay eggs through tough skins into soft fruit and vegetables such as cherries, plums, blueberries, plumcots, grapes, tomatoes, persimmons, sea buckthorn, soapberry, Osage orange and softer fruits such as raspberries, blackberries, mulberries, peaches, figs and kiwi, for example. That egg laying destroys the commercial sale of such crops, for when the eggs hatch, they hatch into maggots. Some farmers on the coast have suffered 20 percent crop losses to this tiny creature.

The males have a single dark spot on the leading edge of each wing, but they’re very difficult to identify since they’re less than one-eighth inch long. Females have a saw-like ovipositor (egg layer), and one female can lay several hundred eggs in her lifetime. She may lay one to three eggs in a single fruit, each with tiny snorkel-like breathing tubes. Both genders have red eyes, pale brown bodies, clear wings, save for the spots on male drosophilas’ wings.

These flies are native to Japan and Korea, and were first discovered in the U.S. in August of 2008 in Santa Cruz County, California. The following year they were found in Oregon, Washington and British Columbia, and were first found in traps in Moscow, Idaho, in 2012. University of Idaho entomologists report these trapped flies were fewer in number in southwestern Idaho, perhaps due to hot, dry conditions. They seem to prefer moist, cooler conditions.

Idaho entomologists in Moscow and Parma are finding the numbers fluctuate, however, growing far higher in population near the end of the growing season. In November, even after freezes, they were still catching a few in traps, even though there were none of the known hosts in the area. Entomologists are searching to discover what else hosts these destructive flies, and learning as much as possible about their lives for control purposes.

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Changes in gardening (and farming) are looming for this coming growing season and beyond. The past few years have seen an emphasis on “sustainable” growing, and now it’s going to be on “restoration,” according to one source. That word isn’t the best that could be used, I think. Maybe “sequestration” would be better.

Now that most nations on earth agree that atmospheric carbon must be reduced for the health of this planet, efforts aim to lower the high carbon levels already in our atmosphere and to diminish that carbon that’s added by human endeavor. Carbon levels now are at about 400 ppm (parts per million) of our atmosphere, and the recent multinational agreement was to reduce that level to at least 350 ppm.

What does that have to do with gardening?

Plenty.

For one thing, there will be an emphasis on wider use of no-till gardening and farming, since tilling earth releases carbon from the soil into the atmosphere. Since bare earth releases carbon and makes soil vulnerable to erosion by wind and water, gardeners and farmers will be urged to grow cover crops instead of letting land lie bare and fallow.

Other advantages to no-till growing include not exposing buried weed seeds to light sparking their germination, and not ripping up the complex web of microscopic fungi and mycorrhizae that have assembled to feed plant roots.

Another enemy of carbon sequestration will be more difficult to eliminate, since it directly involves monetary investment and multinational corporations. That enemy is synthetic fertilizer, used by many gardeners and most farmers. Synthetic fertilizers, unlike organic fertilizers, do not feed or support the soil food web comprised of those millions of protozoa, bacteria, fungi, arthropods and other minuscule critters in the soil that consume or change carbon.

Manufacturers of synthetic fertilizers will complain and fight strenuously to continue selling their products, so brace yourselves. They will lose a lot of money unless they convert their manufacture to organic fertilizers.

There are other advantages to no-till growing, too. Tilling exposes buried weed seeds to light, sparking their germination. Not tilling preserves soil structure and a complex food web and reduces weed emergence.

This story was originally published January 6, 2016 at 12:28 PM with the headline "Margaret Lauterbach: Destructive spotted wing drosophila found in southern Idaho."