SPOTTED ALFALFA APHID, THERIOAPHIS-MACULATA, FATTY-ACIDS RELATIVE TO THE CONDITION AND SUSCEPTIBILITY OF ITS HOST

Fatty acids of spotted alfalfa aphids, Therioaphis maculata (Buckton), were compared to determine what effects host condition and susceptibility to aphids have on fatty acid metabolism. Myristic acid was the predominant fatty acid in aphids that were feeding on newly infested, green alfalfa tissues. In contrast, linoleic acid was the predominant fatty acid in aphids that were feeding on chlorotic leaves 14 days after the plants were infested. Amounts of myristic acid per mg of aphid, examined 14 days after the plants were infested, were ca. 71% less than that for aphids collected from alfalfa 4 days after the plants were infested. Amounts of linoleic acid per mg of aphid live weight did not change over this period. These changes in spotted alfalfa aphid fatty acids were not due to variations in either fatty acid compositions of aphid life stages or alfalfa fatty acids. Ratios of myristic acid to linoleic acid varied in aphids removed from plants 4 days after infestation compared to aphids with which the plants were originally infested. These ratios increased in aphids feeding on alfalfa plants that were susceptible to spotted alfalfa aphids and decreased in aphids feeding on plants that exhibited resistance characteristics of antibiosis and/or antixenosis.