Antistrophus sp.
Rosinweed cryptic stem gall wasp

Hosts: Whorled rosinweed (S. asteriscus var. trifoliatum)

Gall location and description: Galls of species in this group are cryptic, meaning they are not outwardly visible and can only be located upon dissection of a galled stem. When dissected, the stem will have numerous brown, oval-shaped chambers along the inside of the pith, each with a single insect.

Range: This species group has been found throughout the Midwestern, Eastern, and South Central United States. Like many other herb galls, this complex probably occurs throughout the entire ranges of each species’ respective host plant(s).

As with the rosinweed flower gall wasps, it was once believed that cryptic galls on rosinweeds were all induced by either of two species, Antistrophus minor and A. rufus. Recent data shows that there are multiple species of cryptic stem gall wasps on these plants, each preferring a single host plant.

Unlike other rosinweeds, compass plant (S. laciniatum) has been found to host two distinct species of cryptic stem gall wasps. These two species are found in the same habitats, and often induce galls on the same individual host plant. The reason for this bizarre occurrence is currently unknown.

Many unrelated groups of gall wasps seem to have indepdently developed the ability to induce cryptic, inconspicuous galls. The mechanism by which this has been made possible is not known, but it is likely that having hidden galls decreases the odds of attack by predators or parasites. Due to the known diversity of cryptic gall wasps and hidden nature of cryptic galls, it is quite likely that many cryptic galls have thus far evaded detection and await discovery!

- Louis Nastasi, Charles Davis: (2022) Field Guide to the Herb and Bramble Gall Wasps of North America^©