The number of monarch butterflies is declining steeply in North America because farmers destroy the milkweed plant, which is the sole diet of the butterfly's caterpillars. Now agricultural researchers in the US have found uses for milkweed-which could save the butterfly, and the ozone layer into the bargain.
Milkweed is full of toxins called cardenolides. It also produces fluffy, airborne seeds. Farmers hate it, partly because it is so poisonous and partly because the seeds clog the air intakes of farm equipment.
Natural Fibers of Ogallala, Nebraska, harvests the fluff to make felt and stuff pillows. But the poisonous seeds were an unwanted byproduct. Now the US Department of Agriculture's Center for Agricultural Utilization Research in Peoria, Illinois, has found uses for them.
Grinding and pressing the seeds yields oil and a coarse powder or meal. The cardenolides stay in the meal but not the oil, says Rogers Harry-O'Kuru, who led the research. Spreading the meal on the ground kills soil-dwelling crop pests, such as nematode worms and army worms. The meal could replace methyl bromide, which is currently used to control the worms. Methyl bromide is a potent destroyer of the ozone layer and the US has pledged to ban it by 2002. The oil may be useful in skin creams, as it retains water.
Debora MacKenzie
NewScientist, 16 October 1999 No2208 p24
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