Andricus atrimentus, new species
Galls (Pl. XXIV, Figs. 15, 16) - Small, inflated capsules in the leaf-blade. Monothalamous. Spherical, 3-5, mm. in diameter, about smooth, leaf-green when fresh, soon paling, finally drying yellow-brown. Walls thin, a thin-walled larval cell about 1.5 mm in diameter is connected with the outside by a tangle of dense, not not definitely branched fibers. In the leaf-tissue, projecting about equally on either side, usually near the edge of very young leaves of Quercus douglasii.
Range - California: Three Rivers, Redding.
These galls develop early on the unfolding leaves, looking like small air-bubbles blown in the tissue. The galls were always very new and fresh when gathered, but were also practically mature. The development of this generation of the species must be a matter of only a month or two; the other generation is unknown. The adults were maturing, had not emerged, but did emerge at some date later than the dates of collecting the galls: March 23 at Three Rivers, and April 2 at Redding. Of 23 adults, 13 were females. This species resembles Andricus palustris form palustris (Osten Sacken) of the black oaks of the eastern part of the United States, and it might prove desirable to consider the two as varieties of one species. Morphologically the two are very similar, even in many minute details of venation, thoracic sculpture, abdominal and antennal characters; in atrimentus the parapsides are more convergent at the scutellum, the scutellum is less elongate, less rugose, with the foveal groove smoother and less distinctly bifoveate than in palustris. In the male of atrimentus the abdomen is not as small as in palustris. Atrimentus occurs on a white oak in one distinct faunal area; palustris on black oaks in a very different faunal area. It is exceedingly significant that the galls of the two species show similarity of structure, for as has been repeatedly shown the gall is an expression of the physiological nature of the insect. Physiologically then the two species are related,just as they are morphologically, but physiologically they differ even more markedly than morphologically. For though the galls are similar hollow bladders in the leaf, the Pacific Coast species does not have the thick and succulent walls of palustris; while the attached larval cell of atrimentus is distinctly unlike the remarkable, loose cell of palustris.Both forms are bisexual generations, developing very quickly in early spring on the unfolding leaves. The other generation of palustris, namely Andricus palustris form compressus (Gillette), is a wingless, agamic species forming a small, hollow, egg-shaped, separable gall on theleaves in late summer, the gall dropping to the ground in autumn, the insect emerging very early in the spring. It is not unlikely that atrimentus has a similar history, but it will be important that some one determine exactly what differences exist in the life-histories of the two-insects.
