The history of pest management is longer than many think. An outline is provided in the November 1997 issue of Chemically Speaking, newsletter of the Pesticide Information Office, Institute of Food and Agricultural Sciences, University of Florida.
According to the article, the beginnings can be traced back to 8000 BC. As early as 200 BC, the Roman, Cato the Censor advocated oil sprays for pest control and the first rat-proof grainary was built in 13 BC. From 1000 to 1300 AD, Arabians transported cultures of predatory ants to control foliage-eating ants on date palms. Many ideas were developed during Medieval times. In Berne, Switzerland, in 1476 cutworms were taken to court, pronounced guilty, excommunicated by the Archbishop, and then banished. And in 1485, The high vicar of Valence commanded caterpillars to appear before him. He gave them a defense council and finally condemned them to leave the area.
It was not until 1900 that pesticides arrived on the scene. By 1939, the insecticidal properties of DDT were recognized. Shortly thereafter, in 1946 insect resistance to this chemical was first reported. By 1993, the article concludes, more than 504 insect species were known to be resistant to at least one formulation of pesticide and at least 17 species of insects developed resistance to major classes of insecticides. There are also many examples of fungicides, herbicides and rodenticides that no longer work. It comes as no surprise that Varroa also appears to be developing resistance to the one formulation that is legal to use for its control.
Advances in pest management often come from studying one organism and using that information to address the problems of another. Take the American chestnut for example. This quintessential New World tree was many things to many people around the turn of the century, according to Judy Treadwell writing for NCNatural Digest Current Features:
“The reddish-brown wood was lightweight, soft, easy to split, very resistant to decay; and it did not warp or shrink. Because of its resistance to decay, industries sprang up throughout the region to use wood from the American chestnut for posts, poles, piling, railroad ties, and split-rail fences. Its straight-grained wood was ideal for building log cabins, furniture, and caskets. Split-rail fences made from the American chestnut can still be found along country roads throughout the northeast United States and the southern Appalachians. The fruit that fell to the ground was an important cash crop. Families raked up chestnuts by the bushels and took wagon loads of them to sell in nearby towns. The people even cooked the chestnuts for their own use. The bark and wood were rich in tannic acid, which provided tannins for use in the tanning of leather. More than half of the vegetable tannin used by the American leather industry at the turn of the century came from the American chestnut. So important was the American chestnut in the southern Appalachians that some of the major timber operations became subsidiaries of leather companies, which were organized to harvest other species for lumber on land bought to insure supplies of chestnut tannin extract. In addition, the American chestnut was a graceful shade tree found in city squares and on the rural homestead.”
However, according to Ms. Treadwell, in about 1904 a blight was introduced into the United States from Asia. Commonly known as the chestnut blight, Endothia parasitica was first found in the chestnut trees on the grounds of the New York Zoological Garden. It is believed that the fungus was unintentionally introduced into America from Asian chestnut trees that were imported as nursery stock. In spite of quarantines and other programs, within 40 years most of the American chestnut trees in the eastern United States were dead. American chestnut trees killed by the blight comprised 50 percent of the overall value of the eastern hardwood timber stands at that time.
In an attempt to restore the American chestnut, two strategies have been pursued. The first is breeding. This has been a long-term effort, and the American Chestnut Foundation has been established to carry on and help fund this work. As part of this, Chinese chestnut trees have been enlisted in the fight. Their genetic material is being incorporated into American stock, and some successes in this arena have been seen.
Another strategy is associated with a recent discovery of a non virulent strain of the chestnut blight in Asia that causes disease remission when inoculated into affected trees. This strain of the blight is essentially a “blight of the blight” that spreads through trees in the wild. It weakens the original blight, thus allowing the tree to survive. This has been called a “hypovirus,” according to Dr. W.L. MacDonald and S.C. Haynes in “The American Chestnut’s Struggle to Survive a Biological Invader,” Land and Water, September and October 1997. Many strains have been found associated with E. parasitica, some reducing the ability of the fungus to cause disease.
The honey bee, in contrast to the American chestnut, is an organism introduced into this continent. However, recent history of this valuable insect shows some surprising similarities to the situation seen in what was once called the queen of American trees. Arrival of the Varroa bee mite has been responsible for the deaths of not only many managed, but most of the wild or feral colonies of honey bees.
Like the chestnut blight, the Varroa mite arrived from Asia and infested American honey bees, which had no internal defense mechanism. Like the blight, quarantines were not effective and the mites rapidly spread across the continent. Unlike the American chestnut, however, honey bees did have the defense of modern pesticides and a committed cadre of beekeepers to ensure application. How long these chemicals will work or be available, however, is not known.
For honey bees, like chestnuts, the long-term solution to an introduced, exotic organism like Varroa appears to be breeding. Thus, as in the chestnut story, Asian honey bee strains are being screened for resistance or tolerance to the mite. This research is being conducted at the Baton Rouge Bee Laboratory, where about 100 queens from eastern Russia soon will be studied extensively. Some American bees in Mexico, however, appear to be tolerant already.
The Africanized honey bee in Brazil has also been shown to be resistant to the full effects of Varroa. One of the reasons for these differences may be different mite reproductive levels, as seen in various parts of the world. What the apicultural world needs now is the equivalent of the American Chestnut hypovirus that, in conjunction with breeding efforts, will help beekeepers gracefully step off the pesticide treadmill.
Newest information from more recent genetic research suggests that a new technology known as RNA interference will be important in finding a novel way to protect honey bees from Varroa. The same thing might also be in the cards for the American chestnut.
