Antistrophus microseris (McCracken & Egbert, 1922)

Nomenclature: Aylax microseris McCracken & Egbert, 1922

Feeds on: Induces galls on Microseris D. Don

Distribution: United States: California

Antistrophus microseris (McC. & Egb.).

Microseris sp.
Fig 197. Stem swelling, 10-20 mm by 20-30 mm long. Type locality, Stanford CA

Fig 197. On Microseris sp. growing in the grass by the side of the road to foothills back of the campus (Stanford). Galls were collected in spring of 1916 and dead adults were found in the box in November.

Antistrophus microseris
Silverpuff stem gall wasp

Host: Douglas’ silverpuff (Microseris douglasii).

Gall location: On the stem, typically at or above the middle.

Description: These galls are medium-sized, spindle-shaped, rounded swellings of the stems, typically 1-3 centimeters in diameter. Fresh galls are green and fleshy, and older galls are brownish, and rough. Internally, mature galls contain several brown “dividers” that are believed to be constructed by the gall wasp larvae during development; the exact process leading to the development of these dividers is unknown.

Range: This species has only been reported from California. However, this gall has been poorly studied, and likely occurs on other silverpuff species, which could increase the possible range of this gall throughout the Western United States. Similarly, the range of the known host plant, Douglas’ silverpuff, includes Baja California; if this gall were to be discovered in Baja California, the silverpuff stem gall wasp would be the only species of herb or bramble gall wasp known from Mexico.

As mentioned above, this gall is particularly poorly studied, even for herb gall wasps. Some as-of-yet unverified observations suggest that similar galls may occur on other silverpuff species, including other genera such as Uropappus. Whether galls on these hosts prove to be those of the silverpuff stem gall wasp remains uncertain. Galls on Uropappus are addressed at the end of this guide. Thus far, all verifiable observations of this species have occured in April; this must be taken into account if one wants to find these galls. This limited window is likely due to the ephemeral nature of silverpuffs, which have relatively short-lived stems.