Turnip aphids beware! Scientists at the Agricultural Research Service and at Anadolu University in Eskisehir, Turkey, have found that oils from many Turkish medicinal herbs are deadlier to the aphid pests than those currently used in biological pesticides.
Studies at two ARS laboratories in Mississippi--the Natural Products Utilization Laboratory in Oxford and the Small Fruit Research Station in Poplarville--found that essential oils from 17 plant species are more toxic to turnip aphids (Lipaphis pseudobrassicae) than oils of peppermint (Mentha piperita) and rosemary (Rosmarinus officinalis), which are used in the United States as organic pesticides and in broad-spectrum insecticides.
The researchers evaluated essential oils from 25 plant species for toxicity to turnip aphids, which attack collards, mustard, broccoli, cabbage, radish, tomato and zucchini, among other vegetable crops throughout the southeastern United States.
The aromatic essential oils help plants attract or repel insects and fend off heat, cold and bacteria. Obtained from air-dried flowering plants, the oils are used in the pharmaceutical, agrochemical, cosmetics and food industries. Because their bioactive compounds are potentially toxic to insects and mites but relatively safe to humans and wildlife, they've recently become the focus of developers of ecologically safe pesticides.
Plant pathologist David Wedge at Oxford and horticulturist James Spiers and entomologist Blair Sampson at Poplarville, along with Turkish colleagues led by chemist Nurhayat Tabanca, identified essential oils--many from wild plants--that achieve 100-percent kill rates at much lower concentrations than peppermint and rosemary oil.
The researchers found that species of Bifora, Satureja and Salvia are the more promising botanical sources of compounds for new pesticides targeting aphids. The scientists were most impressed by the wild bishop plant, Bifora radians. It yielded the least essential oil, but that oil was by far the most toxic to the aphids.
According to Wedge, future efforts may include collaborations with other universities in Turkey and technology transfer of advanced bioassay techniques for agrochemical research.
ARS is the U.S. Department of Agriculture's chief scientific research agency.