ROLE OF SALIVA IN THE HIGHLY DESTRUCTIVE FOURLINED PLANT BUG (HEMIPTERA, MIRIDAE, MIRINAE)

The fourlined plant bug, Poecilocapsus lineatus (F.), is among the mor e damaging hemipterans, causing immediate and conspicuous lesions at f eeding sites on leaves. The damage appears histologically to involve c omplete loss of cellular integrity and removal of the palisade cell la yer. The ability of P. lineatus to cause such remarkable damage appear s to reside in the chemical nature of its salivary products; however, among tests of the salivary enzymes that included assays for pectinase , cellulase, proteinase, polyphenol oxidase, lipase, and amylase, only an exopectinase was found. The size of the salivary gland complex in later instars and adults (approximate to 14-21% of total body mass) wa s proportionately far greater than that found in other Heteroptera, su ch as in another mirid, Lygus hesperus Knight (where salivary gland co mplexes were only 4-7% of total body mass). Ultrastructure analysis of the salivary glands revealed that the vast majority of the cellular m ake-up of the glands is rough endoplasmic reticulum. A complex of prot eins was present in salivary gland extracts with molecular weights of 87, 79, 42, 33, 30, and 21 kDa. Gel filtration chromatography revealed a major peak of exopectinase activity corresponding to a molecular we ight of approximate to 30-35 kDa; and ion exchange chromatography reve aled 2 peaks of exopectinase activity eluting with an ion strength of approximate to 0.4 and 0.5 M NaCl.