The effects of gall formation by Lipara lucens (Diptera, Cloropidae) on its host Phragmites australis (Poaceae)
Faculty of Sciences. Biology
Biology of Gall-inducing arthropods
International Symposium on the Biology of Cell-Inducing Arthropods, AUG 14-19, 1997, INTER FORESTRY RES ORG, MATRAFURED, HUNGARY
, p. 173-187
University of Antwerp
The flies of the genus Lipara (Diptera, Chloropidae) are monophagous herbivores of common reed, Phragmites australis, on which they induce characteristic cigar-like galls. We investigated the morphological and hormonal changes in the reed shoots during gall development. To this end, Lipara lucens galls of different ages, cultivated in a greenhouse and collected in the field, were examined morphologically, histochemically and biochemically. Shoot elongation is strongly reduced. Ungalled shoots are longer and bear more leaves than galled shoots. Total shoot biomass does not differ between galled and ungalled shoots. Biomass allocated to gall tissues reduces biomass allocated to the rest of the stem and the leaves. Internally, the gall consists of a central marrow zone of rich nutritive cells surrounded by a thickened and lignified tissue cylinder. At the transition zone between the marrow parenchyma and the tissue cylinder, a layer of longitudinal and radial sclerenchyma cells arises during gall development. Vascular bundles from the tissue cylinder branch off to this zone of sclerenchyma cells, connecting the larval chamber with the vascular bundles. In the apical zone of parasitized shoots, the concentration of free indole-3-acetic acid (IAA) decreases in conjunction with an increase of conjugated IAA. At the same time, parasitized stems show a reduced basipetal gradient of free IAA. The altered free IAA/conjugated IAA balance probably plays an important role in the inhibition of shoot elongation. The abscissic acid (ABA) concentration in the apical zone of the gall increases. Probably the latter is due to the presence of the chewing larvae between the young enwrapped leaves above the gall apical region.