Weldia californica, new species
Gall. Monothalamous bud or stem galls occurring singly or in groups of three to five; on current year's growth, if produced directly from stem, but, on two-year-old stem, if produced directly from terminal or axillary bud; galls produced from stems bear two, short, rounded projections at the point of attachment, one on each side of a groove occupied by the stem; galls produced from buds are circular at the point of attachment, often with bud scales clinging to gall base; subspherical in outline and flattened or even dimpled at apex (Q t californica [john-tuckeri]), surface mostly smooth with few irregularities; others circular, with low-level, rounded bumps over surface (Q douglasii).
Internal structure: Mature galls contain a subcentral, oval, larval capsule composed of an inner, nutritive cell layer (may be indistinct in mature galls) and an outer, hardened, protective, sclerenchymal layer; capsulre surrounded by thick zone of large, loosely packed, columnar cells, more compressed and hardened just beneath epidermis; epidermis composed of thin, hardened layer of small, compressed cuboidal cells, two-to-three cells deep, appear crystalline in cross-section.
Size: Average of 100 unparasitized galls: horizontal diameter, 12.2 mm; height, 11.6 mm.
[Type locality: San Bernardino CA]
Host records: Quercus douglasii, dumosa [berberidifolia? or possibly Q dumosa sensu strictu], Quercus turbinella californica [john-tuckeri] and various hybrids of these species and with other [white-group] oaks which are not hosts of W californica in the unhybridized condition. I have never seen galls of W californica on Q durata or lobata and only infrequently on Q dumosa where it occurs in the vicinity of either Q douglasii or Q t californica.
Range: Known to occur only in California from San Diego Co north to Lake Co and probably around the northern rim of the San Joaquin Valley as well, wherever Q douglasii occurs.
Remarks: I at first thought this species to be Disholcaspis canescens while conducting biological studies on a large population at Cajon Pass. Later, I became aware that two distinct species, based on adults, were consistently placed together under D canescens in museum collections. This seemed peculiar since, with the exception of similar abdominal setation, the adults of both species are distinct. Bassett's type adult of D canescens matched the original description, but cotype galls did not and proved to be galls of W californica. Apparently, galls of D canescens, W corallina, and W californica were sent to Bassett in the same shipment from Napa CA and subsequently were mixed. The failure of later works, myself included, to correctly separate these species, is witness to the often misleading reliance placed on gall characteristics which may be only superficial.
Gall growth. Young galls of W californica first appear on Quercus turbinella californica [john-tuckeri] in mid-June as elongate evaginations of new stems or from terminal and axillary buds in which incipient stems were inhibited by early eclosion and larval feeding. These new galls are pale green and bear a dense coat of short, colorless pubescence which generally weathers away as they mature. Initial gall growth is rapid and by 1 August, they are approximately 7-8 mm in diameter, reddish green, and contain a thick-walled larval capsule composed entirely of moist, nutritive tissue closely surrounding the larva. By 15 September, galls are full-sized and average ca. 12 mm in diameter. The outer surface turns a deep red and the surface pubescence begins to weather away. The larval capsule, ca 3.5 mm in greatest diameter, is full-sized by this time and considerably larger than the third instar larva within. Galls are usually mature, medium brown and glabrous by 1 October. Internal tissue is dry and rust-colored and the mature, C-shaped larva completely fills the larval capsule.
Four distinct zones of tissue, ie, epidermis, collenchyma, parenchyma and the sclerenchyma of the larval capsule, may be distinguished in sections through the mature galls. The inner nutritive layer of the larval capsule, the larval food source, is usually indistinguishable in mature galls.
Rearing adults. During October, 1974, mature galls were collected from oak branches at Site No 1 [26 miles northwest of San Bernardino] and maintained outdoors in rearing containers at Riverside, CA. Adult emergence in these containers began on 16 November and continued until 15 December. Emergences were most frequent in the early-morning hours and rare after midday. No emergence occurred on windy days of below-normal relative humidity. The largest number of emergences followed rain and/or periods of heavy fog.
Galls dissected, prior to normal emergence, exposed a variable degree of emergence-tunnel completion. The adult female chews an emergence tunnel leading from the larval capsule to the epidermis, through the side of the gall, midway between apex and the point of attachment to the stem. Many galls contained completed emergence tunnels except for a thin epidermal layer that separated the insect from the outside environment. During periods of subnormal relative humidity, females were found resting, sometimes for several days, just beneath this epidermal "window." Once she began chewing, the female could exit the gall within an hour. Many galls that bore no exit hole after the normal emergence period ended contained dead females in partially completed emergence tunnels.
[Burnett gives a description of the results of oviposition experiments, detailing when and where the female oviposits]
Early egg eclosion occurs before new stems begin to grow beyond the bud scales and results in the complete inhibition of normal plant tissue development in the bud. Consequently, galls appear to arise directly from within the bud. On 27 May, such galls were 1-2 mm in diameter, pale green, and spherical with an apical red nipple. Buds become laterally distorted as galls enlarge to occupy the entire bud base. On 14 June, small galls were observed growing from buds on year-old wood, not growing directly from within a bud. Late eclosion occurring after new stem growth has begun results in true stem galls, as the eggs or larvae are carried away from the area of original egg deposition.
[From key to galls, page 176 of the pdf]
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Subglobular stem and leaf petiole galls without apical projection or strong surface tubercles; surface may be smooth or bumpy
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Stem galls on white oaks of the Pacific Slope from northern Baja California to points north; larval capsule spherical or oval, positioned centrally or basally in parenchymal tissue; under 14 mm in diameter.
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Outline symmetrical, larger apically; larval capsule oval, basally positioned in parenchymal tissue; surface smooth or slightly bumpy; occurs in California on Q douglasii, Q dumosa, and Q turbinella californica [john-tuckeri]
