Dryocosmus dubiosus (Fullaway)

Laboratory experiments show that adults of Dryocosmus dubiosus (Fullaway) reared from ament galls of the California live oak, Quercus agrifolia Nee, are bisexual. The females from this generation oviposit in the leaf veins of black oaks where they produce an agamic generation of females in characteristic bicornate galls. The females produced in these leaf galls were formerly thought to be Dryocosmus bicornis (McCracken and Egbert), but now must be considered as the agamic generation of D. dubiosus. The agamic generation is composed of two types of females, one producing only males and the other producing only females. Both generations are attacked by the parasite, Torymus fullawayi (Huber).

Agamic generation: Dryocosmus bicornis (McCracken and Egbert) was described from females cut from characteristic bicornate galls which occur on the veins on the lower surface of the leaves of Q agrifolia. The adults are all females, and are distinct from the females of D dubiosus that are bred from ament galls. The morphological differences account for their original placement in separate genera. D dubiosus was first described as a species of Diplolepis, and later it was transferred by Felt (1940) to Dryophanta. On the other hand, D bicornis was originally described as a member of the genus Callirhytis. Both species were later correctly placed in Dryocosmus by Weld (1951, 1952, 1957).

The results of breeding experiments now indicate that the supposedly separate species are in reality alternating generations of a single species. Because of priority the name to be given this single species is Dryocosmus dubiosus (Fullaway), although it does seem unfortunate to discard the particularly descriptive "bicornis."

Dryocosmus bicornis

Quercus agrifolia, wislizeni
Leaf galls, detachable
Fig 113. Single, on vein, under side.

Fig 113: Occur in fall on under side of leaf. Have been known to be so numerous they have been collected by the quart on a sheet spread under the tree. Leaves turn yellow and drop and trees look ragged in winter.

Dryocosmus dubiosus

Fresh galls of this unisexual generation are green and measure 3 mm long. Dozens of these galls can occur on a single leaf.