Baccharis gall fly—Rhopalomyia californica
The baccharis gall fly, or gall midge (Cecidomyiidae), causes fleshy, knoblike swellings or galls on the shoot tips of coyote brush, Baccharis pilularis.
Baccharis gall fly adults are delicate flies about 1/16 inch long with long, slender legs and antennae. The tiny reddish eggs are found on growing terminals. Larvae are orange maggots, up to 1/10 inch long, and occur in galls.
Baccharis gall mite, Aceria baccharices, also galls coyote brush. It causes small, beadlike swellings or raised blisters on leaves. The leaf may be deform if galls are numerous. The bead galls are open on the leaf underside where the mites feed in groups. The tiny eriophyid mites are elongate, carrot- or wedge-shaped, and 1/50 inch long or smaller; a microscope is required to clearly distinguish them.
Baccharis gall fly females lay eggs on actively growing terminals. The larvae hatch and enter the plant between bud scales, then gall formation begins. Galls are multichambered (one midge larva per chamber) and contain from one to as many as 100 chambers per gall.
Larvae pupate inside the gall. The adults emerge, mate, and live only a few days. Development from egg to pupa takes one month or more. The midge has several generations per year and can be active year round if temperature and host plant growth are favorable.
Feeding by baccharis gall fly larvae causes galled (swollen) shoot terminals, which stop growing in length.
Plants are not killed by baccharis gall flies. Tolerate galling on plants. Many species of beneficial parasites attack gall fly larvae; conserve natural enemies. There are no known artificial controls.