St John's Wort Gall Midge

Cecidomyiidae

Zeuxidiplosis

Hypericum concinnum

California

Hypericum perforatum

Arkansas

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Idaho

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Indiana

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Zeuxidiplosis giardi

Swollen bud... *Zeuxidiplosis giardi* (Kieffer)

Buds are ovoid, slightly pointed at the tip; the terminal leaves are incurved, swollen, and usually red. Larvae may be gregarious, and pupation occurs in the bud...The gall midge has apparently crossed over to a native American *Hypericum*. Hosts: The alien *H. perforatum* and the native *H. concinnum*...

The plant-feeding gall midges of North America

The topmost leaf pair of a sterile stem is strongly thickened, broadened and shortened, often also coloured red, and forms a spherical gall. 

Plant Parasites of Europe

Zeuxidiplosis giardi
Hosts
St. Johnswort (Hypericum perforatum)

Description
Larvae are orange and can reach up to 2mm in length, completing three instars. Adults are very small (3 mm long) and have dark red bodies and gray heads, wings, and legs.

Life Cycle
Larvae emerge in early spring and feed on leaf buds, causing leaves to grow into a spherical gall that is green with reddish markings. Larvae feed at the base of the gall; pupation occurs inside. Adults are sexually mature upon emergence and live for only 5 days. There may be up to 7 generations per year, though there are usually fewer than 5. Larvae and pupae overwinter.

Impact
Larval feeding and galling lead to stunted plant growth and occasional death, though it is not as effective in the western U.S. as other agents.

Availability
Limited availability from California and Hawaii.

... Author: Rachel Winston, Mark Schwarzlander. University of Idaho Extension.

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