Baccharis gall fly—Rhopalomyia californica
Feeding by larvae of baccharis gall fly, or gall midge (family Cecidomyiidae), causes knoblike swellings (galls) on the shoot tips of coyote brush, Baccharis pilularis.
Identification
Baccharis gall fly adults are delicate flies about 1/16 (1.5 mm) inch long with long, slender legs and antennae. Adult females with eggs have a swollen, orangish to reddish abdomen. Females that have laid all their eggs and males have a more slender abdomen and are gray to pale colored overall. The tiny reddish eggs can be found on terminals and scattered along shoots.
Larvae are orangish maggots up to 1/10 inch (2.5 mm) long. They occur in individual chambers in galls that are generally comprised of numerous chambers, each containing one immature gall fly. After the larvae complete their development, pupate, and emerge as adults, elongate, translucent to white cast skins of the fly may be seen protruding from each of numerous tiny holes in the gall.
Life cycle
Baccharis gall fly develops through 4 life stages: egg, larva, pupa, and adult. Adult females lay eggs on actively growing terminals. The larvae hatch and chew into the plant between bud scales. Once larvae start feeding, the surrounding plant tissue begins to swell into a gall. Most galls have multiple chambers with 1 midge larva per chamber and a single gall with up to about 100 chambers.
After larvae mature they pupate within the gall. Shortly before the adult emerges, the pupa chews a hole in the gall and may partly protrude. The pupal covering then splits and the adult emerges, leaving the cast skin attached to the outside of the gall. The gall midges then mate, and adult females lay eggs. Each adult midge lives only about 2 days or less.
Development from egg to adult happens in about 1 month when temperatures are warm. Midge development and reproduction can continue throughout the year where winters are mild. Baccharis gall fly has several generations per year.
Damage
Feeding by larvae of baccharis gall fly causes infested tissue to swell into globular galls. The galls are commonly green but can also be pinkish or red. Old galls may become brown and dry.
Galled terminal shoots stop growing in length, which can give plants a bushy appearance. Although somewhat unsightly, the galls when green can be overlooked among the green foliage and stems. Baccharis gall fly does not threaten the survival of coyote brush.
Solutions
Many species of beneficial parasitoid (parasitic) wasps attack larvae of baccharis gall fly. There are no known direct control options, and no control efforts are recommended.
Adapted from Observations on Rhopalomyia californica Felt (Diptera Itonididae), University of California Agriculture and Natural Resources and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM). |
Galls of baccharis gall fly.
Gall of baccharis gall fly.
Adult female of baccharis gall fly on a galled coyote brush terminal.
White pupal cast skins of baccharis gall fly on a galled coyote brush terminal.
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