Injury caused by Lygus hesperus Knight is due principally to the enzymatic digestion of the plant’s tissue by polygalacturonase secreted during feeding. A limited amount of mechanical injury may result from feeding. L. hesperus is unable to synthesize indoleacetic acid and is also unable to secrete plant hormones in its saliva after having ingested these hormones in its diet. The type of damage associated with feeding, i.e., necrosis, abscission of reproductive organs, “blasting,” “cat facing,” or reduction of vegetative growth, depends upon the size of the organ fed upon and the specific site of feeding. If feeding results in the destruction of specific hormone producing sites, the resultant damage is in accord with the known physiological responses of plants to hormonal manipulation.