Lygus hesperus and L. lineolaris (Hemiptera: Miridae), Phytophages, Zoophages, or Omnivores: Evidence of Feeding Adaptations Suggested by the Salivary and Midgut Digestive Enzymes2

Abstract

Although Lygus hesperus Knight and L. lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) are extremely destructive pests of a large variety of crops, the exact nature of their feeding adaptations remains unresolved. We studied the digestive enzymes in the salivary gland complex and guts of L. hesperus and L. lineolaris to elucidate the feeding mechanism and to determine the relative zoophagous and phytophagous potential of each species. Most of the digestive enzyme activity in both species originated in the salivary gland complex rather than the gut. We found general protease activity in the salivary gland complexes and guts of both species, with the predominant activity in the salivary gland complexes. Trypsin-like enzyme activity was the predominant alkaline protease in both species, but L. hesperus had significantly more activity than did L. lineolaris. In both species trypsin-like activity was greater in the salivary gland complex than in the gut. Some elastase-like activity occurred in both body regions of both species, and there was no chymotrypsin-like activity in either body region of either species. Both α-amylase (EC 3.2.1.2) and pectinase (EC 3.2.1.15) were present in both regions but were predominant in the salivary gland complexes of both species, but activities of both enzymes were significantly greater in L. lineolaris than in L. hesperus. Both species lacked α-glucosidase (EC 3.2.1.20) in the salivary gland complex, but both had considerable activity of this maltose-and sucrose-digesting enzyme in the gut. Also, both species had phospholipase C (EC 3.1.4.3) activity in the gut but none in the salivary gland complex. Both species had very low to negligible lipase (triacylglycerol lipase, EC 3.1.1.3) contents in the gut and no measurable lipase in the salivary gland complex. Hyaluronidase (3.2.1.35) activity was lacking in both species' salivary glands and guts. These enzyme profiles suggest that both species are well suited for phytophagy, but that L. lineolaris may be slightly better suited to strict herbivory.