Mitodiplosis graminis induces a stem gall on Ehrharta villosa (Fig. 1). The leaf blades on an infested stem become shortened, the stem internodes do not lengthen, and the leaf sheaths are thickened and widened, creating a witch’s broom-like structure (Figs 1a, c). The superficial tissue layers of the gall (i.e. malformed leaf sheaths and blades) become grey and senescent while the internal tissue (i.e. malformed stem) stays soft and green (Fig. 1c). There are 2–20 larvae, and later pupae, inside separate larval chambers within the malformed stem tissue (Fig. 1b). Galls with more larvae are longer than those with fewer larvae. The malformed stem eventually grows out so that it protrudes from the leaf sheaths (Fig. 1c) enabling an unhindered emergence of the gall midge from the stem’s surface (Fig. 1d).

In South Africa, the gall midge Mitodiplosis graminis Kieffer induces stem galls on E. villosa var. villosa (Kolesik and Wood 2019). They also reported that the large, empty larval chambers left by the midge were occupied by A. woodi, a host-specific, gall-forming nematode [not thought to be the gallformer in this case].