There are over 800 species of cynipid wasps, most of which use oak trees as their egg-laying sites. The red cone gall is induced by the cynipid wasp Andricus kingi.
Red cone galls occur on the leaves of blue, Oregon and valley oaks (white oaks). These monothalamous (having a single chamber) galls are indeed red and cone-shaped. They arise from a flared, cup-shaped base that is narrowly attached to the leaf, making the gall easily detachable. The apex is pointed and blunt-tipped. Red cone galls can occur singly or multiply on both surfaces of the leaf.
The A kingi cynipid wasp exhibits alternation of generations (heterogeny). The sexual generation emerges in the spring after overwintering as prepupae inside the galls. Both male and female wasps emerge in the spring. The females lay eggs one at a time on emerging leaves. With the egg the female also releases a substance that stimulates the leaf to develop protective tissue around the egg. The larvae have chewing mouth parts that break the leaf cell walls to get at the cell juices. As the larvae begin to eat the leaf they also release chemicals that change the protective shell into a gall. The larva pupates within the gall and emerges as an adult wasp. Adult cynipid wasps live for about a week, without eating, until they mate, find a suitable host and lay eggs.
Only females develop from the eggs laid by the sexual “spring generation”. These females lay eggs parthenogenetically, that is, without male fertilization. Each offspring is a clone of the mother. This asexual “summer-fall” generation then overwinters.
The galls developed by the sexual generation are different in appearance from those induced by the asexual generation. These red cone galls were photographed in September at the John Muir National Historic Site in Martinez CA and are the product of the “summer-fall” asexual females.
The intestines of A kingi are closed for most of the larval life. Before pupation, the gut opens and emits liquid wastes which are absorbed by the gall tissues. There is no evidence of solid waste within the red cone gall chamber.
Now Leonard and I have another “quest”: we need to find sexual A kingi galls.