Bassettia ligni
Bisexual generation

[Photos of this gall appear on page 6 of the pdf]

GALL (Figs. 7, 8). Inconspicuous blister-like swellings in the blade tissue of mature leaves, seldom near the margins or in the veins. Mature galls are approximately 4 mm diam., but only about 2 mm are visible on the top surface of the leaf as an indistinct subcircular swelling, slightly brown-puckered off-center. Living galls are more noticeable on the underside of the leaf where the swellings are more pronounced, slightly smoother and paler than the surrounding tissue, and with dimpled centers (Fig. 7). Adults normally emerge from the upper surface, leaving rough subcircular exit holes that soon develop elevated margins (Fig. 8). These holes become more conspicuous as the leaves die. Galls may contain 1-4 cells and are frequently confluent; polythalamous galls more often contain males. Individual leaves may have 1-30 galls.

Adults of the bisexual generation emerge during late June to mid-July. Males wait on nearby leaves for females to emerge. Adults are most active during mid-day. Females oviposit on 2- to 5-year-old stems, often on their host tree in the areas where the agamic generation emerged earlier in the year. The pupal stage develops by September.

Quercus douglasii, lobata
Leaf galls, integral
Small parenchyma thickenings in numbers like Fig 139.

Bassettia ligni

On May 20, 1966, an undescribed leaf gall (Fig. 1 a), from which both male and female Cynipidae were emerging, was found on Q. lobata at Locke, Sacramento County. The females readily oviposited in twig growth of the previous year when confined on Q. lobata seedlings in the laboratory. The galls which appeared in the fall of 1966 were those of B. ligni (Fig. 1 b). This species is also known to occur on Q. douglasii Hooker & Arnott and on Q. dumosa Nuttall (Weld 1957a). The galls of the bisexual generation appear as very slight oval swellings protruding from both leaf surfaces. They remain green even when mature. The adult emergence hole is found at either end of the oval gall, but always on the upper leaf surface. These monothalamous galls sometimes occur singly but are usually found in pairs. The average dimensions are 1.53±0.14 mm long by 0.90±0.03 mm wide. We believe them to be the same as the galls Weld (1957a) described as "like those of Neuroterus engelmanni Kinsey."

Bassettia ligni Kinsey, 1922

Biology--Alternate asexual and sexual generations are known. The asexual generation induces integral leaf galls while the sexual generation stimulates stem galls on Q. douglasii, dumosa, and lobata. The adults of the sexual generation emerge from leaf galls during June to mid-July; the adults of the asexual generation emerge from the bark during mid-April.

Distribution--CA, OR