oak rough bulletgall wasp

Oak rough bulletgall wasp is a cynipid gall wasp. It is usually identified by the gall it produces. In Minnesota, galls are found in clusters on the twigs and branches of bur oak and swamp white oak. They first appear as green bumps on the twig. The bumps later turn bright red. As they grow into round galls, they turn light brown and are soft. Eventually, they turn dark brown and harden. Mature galls are 5 ⁄16″ to ⅝″ in diameter, woody, and spherical, with a nipple-like, obscure point at the top. They produce honeydew that attracts bees, and wasps, and ants, which protect the gall wasp from other parasitic wasps. Each gall contains only a single wasp, though they may be shared by other species (inquilines). A small, circular hole in the side of a gall indicates where the wasp has emerged.

The galls remain on the tree up to five years after the wasp has left the gall. They do not kill the host stem but will reduce the growth of the infested tree.

Galls: 5 ⁄16″ to ⅝″ in diameter

Anywhere the host species are found

One generation per year, late October to early November

The life cycle of this wasp involves alternation of generations, one generation with only asexual females and one generation with both sexual males and sexual females. Information is only available for the asexual generation. The sexual generation has not been described in entomological literature.

The female lays eggs in a dormant, terminal bud at the tip of a twig. In the late spring of the following year, the larva stimulates the growing stem to produce a gall in which the wasp develops. The larva pupates within a small cell in the center of the gall. In Minnesota, adults emerge in September. In the asexual generation, both winged and wingless females are produced. Males are unknown.

bur oak, swamp white oak

Adult wasps do not feed

Sources

7, 24, 27, 29, 30, 82, 83.

Common

Oak bullet galls & ants
Waterman's STNY Nature

Alfredo Colon
8/7/2022

Location: Albany, NY

Alfredo Colon
8/6/2022

Location: Albany, NY

Location: hedgerow at Barnes Prairie, Racine Co., WI

Many galls on this particular bur oak, which was sapling size.