Another cynipid wasp that induces a fascinating gall on blue oaks and Oregon white oaks (Quercus garryana) is the sunburst gall wasp (Andricus stellaris). As with the ball-tipped gall wasp, another cynipid wasp featured in my last post (see “Ball-tipped Gall Wasp” on 09-10-14), the life cycle of the sunburst gall wasp is not well understood.
A. stellaris induces round, convex galls on the undersides of the host leaves. The galls are located between the lateral veins, often near the leaf margin. Sometimes these monothalamous (single-chambered) galls occur in groups. Sunburst galls are white, pink and/or red with a central larva chamber that is darker in color. Crystalline projections radiate laterally and downward from the gall. The upper projections originating near the larval chamber are usually shorter than those near the base. The projections near the base appear club-tipped. I think the sunburst gall resembles a mini-volcano. This gall easily breaks off from the leaf.
Many plant galls become filled with the solid larval waste that accumulates in the gall chambers as the larvae eat and grow. Interestingly cynipid wasps have intestines that are closed. Just before pupation the gut opens and emits liquid wastes into the gall. These liquid wastes are likely absorbed by the gall tissues. The galls of cynipid wasps are not filled with solid waste material.
These sunburst galls were on Oregon white oaks next to Crystal Lake (Shasta County CA). To me the wide variety of galls and their unusual structure are interesting, even if not much is known about their inducers.