Morphological and histochemical analysis of galls of Lipara lucens (Diptera, Chloropidae) on Phragmites australis (Poaceae)

Lipara lucens Meigen (Diptera, Chloropidae) is a monophagous herbivore of t he common reed, Phragmites australis Cav, (Trin.) ex Steud. (Poaceae), on w hich it induces typical cigar-shaped galls. In this paper, the anatomy and histochemistry of galls, cultivated in a greenhouse and collected in the fi eld, were examined. Gall growth takes place while the larva feeds outside t he actual developing gall. During gall growth, internode elongation is redu ced. Internally. the pith parenchyma, destined to become the nutritive tiss ue, proliferates instead of degenerating as is seen in uninfested stems. Th e tissue cylinder around the gall chamber widens up to three times its norm al size, while the pith parenchyma doubles its width. The central pith of n utritive cells becomes surrounded by an inner layer of longitudinal and an outer layer of radial parenchymatous cells. Vascular strands, likely connec ted to the vascular tissue of the host plant, run through this special band of parenchyma cells. The bundles are oriented perpendicular to the stem ax is, surrounding the larval chamber. When the gall is completed, the larva g naws through the growing point and enters the gall chamber, where it consum es the nutritive tissue. A sclerenchymatization process starts now resultin g in an extremely hardened gall. Histochemical staining reveals the presenc e of proteins, DNA, RNA, and a gradient of lipid globules in the nutritive tissue. No starch was detected.