Dryocosmus dubiosus (agamic)

Dryocosmus dubiosus (sexgen)

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 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).

Bisexual generation: Dryocosmus dubiosus (Fullaway) was described in 1911 as a gall maker on the staminate aments of the Coast live oak, Quercus agrifolia Nee. Later it was reported by McCracken and Egbert (1922) as also making galls on the edges of leaves. Weld (1957) extended the host range to another black oak, Quercus wislizenii A.DC. Field observations have shown that the leaf galls are formed only on the very young and tender growth that appears early in the spring and accompanies the production of the male flowers. These galls cause a very severe distortion of the tender leaves and may cause them to wither and die. The galls on the aments and new leaves develop very rapidly and give rise to the bisexual generation of D dubiosus. In 1958 the galls on the aments were first noted in February and emergence of both sexes of the wasps occurred in the laboratory during the first week in March. Trees growing on north-facing slopes, at higher elevations, or in deep, cool canyons were delayed in flowering, and galls containing larvae and prepupae were collected from such locations as late as the first week in May. Although precise quantitative data are lacking, it appeared evident that the peak of the bisexual generation had completed its emergence before the middle of April, and collections after that date consisted only of stragglers from the retarded growth locations. 

Heterogony in Dryocosmus (Hymenoptera, Cynipidae)