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

Abstract

Lipara lucens Meigen (Diptera, Chloropidae) is a monophagous herbivore of the common reed, Phragmites australis Cav. (Trin.) ex Steud. (Poaceae), on which it induces typical cigar-shaped galls. In this paper, the anatomy and histochemistry of galls, cultivated in a greenhouse and collected in the field, were examined. Gall growth takes place while the larva feeds outside the actual developing gall. During gall growth, internode elongation is reduced. Internally, the pith parenchyma, destined to become the nutritive tissue, proliferates instead of degenerating as is seen in uninfested stems. The tissue cylinder around the gall chamber widens up to three times its normal size, while the pith parenchyma doubles its width. The central pith of nutritive cells becomes surrounded by an inner layer of longitudinal and an outer layer of radial parenchymatous cells. Vascular strands, likely connected to the vascular tissue of the host plant, run through this special band of parenchyma cells. The bundles are oriented perpendicular to the stem axis, surrounding the larval chamber. When the gall is completed, the larva gnaws through the growing point and enters the gall chamber, where it consumes the nutritive tissue. A sclerenchymatization process starts now resulting in an extremely hardened gall. Histochemical staining reveals the presence of proteins, DNA, RNA, and a gradient of lipid globules in the nutritive tissue. No starch was detected.Key words: plant-insect interactions, Lipara lucens, Phragmites australis, gall structure.