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Herbicide use is destroying butterfly population

June 9th, 2014 9:12 am by Frances Lamberts

Herbicide use is destroying butterfly population

Frances Lamberts with milkweeds plants in the Ardinna Woods Arboretum. Tony Duncan/Johnson City Press

“When you see an old field,” writes ecologist Craig Holdrege, “the robust common milkweed plants stand out among the much sleeker grasses, asters or goldenrods.”
They are the main food source for the monarch butterfly, and with other milkweed species, the only type of plant on which its caterpillar young can feed and develop. These ingest and retain in their body tissue the plant’s bitter-tasting sap, which throughout the butterfly’s life cycle makes it unpalatable to birds and other predators. Toxins in the sap even help the caterpillar to fight infection; the journal Science last year noted the monarchs “medicate their young” by selectively laying eggs on milkweed plants with the highest amount of the toxins.
Holdrege describes Asclepias syriaca, the common milkweed, as “a remarkable plant.” Its shoots grow from buds on stout underground rhizomes in late spring, thick stems sprout opposite-paired leaves, each higher pair larger and offset by about 90 degrees from the pair below it. Some three to a half-dozen spherical flower clusters develop along the upper stem in late May or June, each containing from dozens to perhaps more than hundred individual, lavender flowers.
Sipping at the nectar-rich, fragrant flowers is how we typically see monarch butterflies in summer, during the milkweed’s month-long flowering time. A variety of other butterflies, native bees and honeybees, nocturnal moths, ants and many other insects also feed on the ample nectar, pollinating the complicated, “hood-and-horn” floral structures along the way.
Seeds take a long time, three to four months, to develop, in a pod covered with soft prickles. To naturalist writer Henry D. Thoreau, describing them in his last written work (Faith in a Seed), they were among “nature’s granary” wonders. Densely confined in a “faery-like casket,” each seed is attached to a silky thread for nourishment from the parent plant until “weaned.” When the seeds finally mature, the pod bursts open and the silk threads parachute them away in a breeze.
The monarch and other nectar-gathering pollinators represent only a minority of animal life for which the common milkweed provides food and microhabitat. From rhizome, stem pith and leaves to sap and seeds — all its parts are primary larval food for several bug and moth and beetle species, an aphid, fly and weevil, as, of course, the monarch’s larvae. Apart from known primal food relationships like these, during a summer survey biologists have documented more than a hundred beetle species and 45 species of bugs interacting with this truly multipurpose plant. It draws to it, as Holdrege remarks, a phenomenal abundance of insect life.
Unfortunately for all these creatures and the monarch butterfly, common milkweed, with its expansive foliage, is among the agricultural-herbicide targeted, broad-leaf weeds. Beginning in the early 1990s, major food crops like corn and soybean were genetically modified by chemical manufacturing companies to withstand frequent spraying with the glyphosate herbicide, for example, with anticipation that through killing the weeds it would save farming labor and raise crop yield.
The herbicide-resistant GM crops soon came to dominate the U.S. industrial-agriculture landscape. Increasing from 7 percent to 88 percent of all planted corn and exceeding 90 percent of all planted soybean, the area under these two crops alone reached 175 million acres last year, as documented the Animal and Plant Health Inspection Service of the Department of Agriculture.
Effects of the loss of its primary food source on the monarch butterfly soon became evident. Conservation organizations that track its yearly migration between North America and the highland forests in Mexico where it overwinters saw an alarming trends picture emerging: As herbicide usage in the United States agriculture heartland rose year by year, the forest area occupied by winter-hibernating monarchs dwindled dramatically.
As this paper reported on Jan. 30, last winter they covered just slightly more than a half-hectare of forest, a 44 percent decrease from the previous record low the year before. Compared to their peak migration in the mid 1990s, 96 percent fewer monarchs successfully reached the wintering grounds last year across the now milkweed-barren U.S. landscape.
The former opinion editor of this newspaper, Tom Hodge, called monarch butterflies his “pets” on account, primarily, of the natural wonder of their 4,000-kilometer migration feat. In an article before his death, Hodge wrote, “If everyone who lives in a house in this nation could dedicate one square yard of his lawn to milkweed plants,” the monarch’s feeding and breeding habitat might be restored and its alarming population decline reversed.
Toward such a beginning, 30 potted plants from one of two common-milkweed colonies in Jonesborough’s Ardinna Woods Arboretum will be given away to area homeowners who would follow Hodge’s urging. Gardeners who wish to obtain a free plant, available during the week of June 8-13, should call Frances Lamberts at 753-5288 or Virginia Causey at 753-1030.
Concerned citizens also may wish to take political action related to this issue. The Environmental Protection Agency is seeking public comment, through June 30, on a pending regulatory decision: Approval of a further defoliant herbicide, developed by the Dow Chemical company, for new, additional GM corn and soy crop varieties.

Frances Lamberts is coordinator
of Ardinna Woods Arboretum
in Jonesborough.

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