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Oak Insects
One
of the most obvious insects on the oaks are Oak
Moths. Click here to
read more about these defoliating moths.
We
can hardly claim to discuss life in an oak if we don't mention the
Cynipid wasps.So many organisms would like to have a slice of oak,
it is amazing. These include woodpeckers, insects, bacteria, fungus,
and viruses.Sometimes, some of the larger animals bring on the smaller
ones. For instance, wasps can introduce bacteria that cause oaks to
drip black, sticky sa (IHRMP
Sheet 61).
Wasps in the family Cynipidae (Cynipid wasps)
are diverse, with many species (~150 that live on oaks).Over 80% of the
wasps in this family use oaks.Many kinds of these wasps specialize on
only one or a few species of oaks. Blue oaks (Quercus douglasii) are host to
many bizarre galls caused by Cynipid wasps. These stingless wasps, often only
millimeters long, produce the galls in a complex way. Galls provide home and
food for these wasps, from the egg to the adult stage. The larvae are inserted
in a particular place (root, acorn, bark, leaf, flower, etc.) where they hatch
from an egg and starts to chew. Saliva from the larvae triggers particular kinds
of strange growth in the oak. Each kind of gall wasp produces a recognizable
gall. How the saliva of a larval wasp induces oak tissue to form tiny balls,
or sea-urchin like growths (etc.) is not well understood. It may involve hormones,
RNA, or viruses in the saliva. Larva eventually chew their way outside the gall
by the fall, and go on to lay more eggs. Some of these gall fall off
the leaves, and the living larvae's movements make the galls move; they
are known as "jumping
galls" and they have a fascinating
story (with photos).
 |
Jumping gall wasp. These gall can be common in California's Valley Oaks. They are produced on the leaves and can fall to the ground under the tree. |
For a great discussion of insects, oaks and galls, see:
Keator, G. 1998. The
Life of an Oak. California Oak Foundation, Heyday Books, Berkeley, CA.
Russo, R. A. 1979. Plant Galls of the California Region . Boxwood Press,
Pacific Grove, California
The system of galls, oaks, and cynipids wasps includes specialized insect predators or competitors that eat the galls stimulated by others. Oaks are not without defense against insects. Oaks produce a variety of chemicals to repel those would munch on them. These include tannins, terpenes, and isoprenes.