Lygus hesperus and L-lineolaris (Hemiptera : Miridae), phytophages, zoophages, or omnivores: Evidence of feeding adaptations suggested by the salivary and midgut digestive enzymes

Although Lygus hesperus Knight and L. lineolaris (Palisot de Beauvois) (Hem iptera: Miridae) are extremely destructive pests of a large Variety of crop s, the exact nature of their feeding adaptations remains unresolved. We stu died the digestive enzymes in the salivary gland complex and guts of L. hes perus and L. lineolaris to elucidate the feeding mechanism and to determine the relative zoophagous and phytophagous potential of each species. Most o f the digestive enzyme activity in both species originated in the salivary gland complex rather than the gut. We found general protease activity in th e salivary gland complexes and guts of both species, with the predominant a ctivity in the salivary gland complexes. Trypsin-like enzyme activity was t he predominant alkaline protease in both species, but L. hesperus had signi ficantly more activity than did L. lineolaris. In both species trypsin-like activity was greater in the salivary gland complex than in the gut. Some e lastase-like activity occurred in both body regions of both species. and th ere was no chymotrypsin-like activity in either body region of either speci es. Both alpha-amylase (EC 3.2.1.2) and pectinase (EC 3.2.1.15) were presen t in both regions but were predominant in the salivary gland complexes of b oth species, but activities of both enzymes were significantly greater in L . lineolaris than in L. hesperus. Both species lacked alpha-glucosidase (EC 3.2.1.20) in the salivary gland complex, but both had considerable activit y of this maltose- and sucrose-digesting enzyme in the gut. Also, both spec ies had phospholipase C (EC 3.1.4.3) activity in the gut but none in the sa livary gland complex. Both species had very low to negligible lipase (triac ylglycerol 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 lacki ng in both species' salivary glands and guts. These enzyme profiles suggest that both species are well suited for phytophagy, but that L. lineolaris m ay be slightly better suited to strict herbivory.