The phytophagous heteropteran, Lygus hesperus Knight was analyzed to determine the distribution of fatty acids among lipid classes in laboratory-reared adults (newly eclosed and 5 day-post eclosion) and in field-collected adults. Profiles of lipid classes varied with source of the insect (field vs. diet-reared), age and sex. Total lipids (% dry wt.) ranged from 5.3 to 30.3% in field-collected males and 5 day-post eclosion diet reared females, respectively. Except for field males the predominant lipid class was triacylglycerols (up to 90% of the total lipids) with phospholipids generally the second most abundant lipid class. The most abundant fatty acid in all classes and all treatments was oleic acid (C18:l ω 9). There were significant differences between the field collected vs. diet-reared insects with respect to concentrations of linolenic acid (C18:3 ω 3), with this polyunsaturated fatty acid being much more abundant in field-collected insects than in diet-reared ones.