Role of saliva in the highly destructive fourlined plant bug (Hemiptera: Miridae: Mirinae)

The fourlined plant bug, Poecilocapsus lineatus (F.), is among the more damaging hemipterans, causing immediate and conspicuous lesions at feeding sites on leaves. The damage appears histologically to involve complete loss of cellular integrity and removal of the palisade cell layer. The ability of P. lineatus to cause such remarkable damage appears 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) was proportionately far greater than that found in other Heteroptera, such as in another mirid, Lygus hesperus Knight (where salivary gland complexes were only 4-7% of total body mass). Ultrastructure analysis of the salivary glands revealed that the vast majority of the cellular make-up of the glands is rough endoplasmic reticulum. A complex of proteins 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 weight of approximate to 30-35 kDa; and ion exchange chromatography revealed 2 peaks of exopectinase activity eluting with an ion strength of approximate to 0.4 and 0.5 M NaCl.