Internal feeder (Coleoptera: Brentidae) in Osmorhiza

This weevil forms spindle-shaped galls on Osmorhiza stems. I have observed the galls beginning as early as mid-May in the study area.

The galls on at least some plants are initially solid inside, but once the egg hatches, the weevil larva begins to excavate the gall interior. In 2017, I found larvae in their tunnels inside galls in early- to mid-July, and a pupa in a gall on 21 July. I also found an adult inside a galled stem on 16 July (image 349-12); the adult was not inside the gall itself, but in a tunnel in an adjacent region of the stem that connected directly to the hollowed-out gall interior. I reared an adult from another gall on 10 August.

I have also reared parasitoid wasps from overwintered galls (images 349-18 through 349-23), and found an apparent brentid pupa in a tunnel in an Osmorhiza basal leaf petiole in mid-October (image 349-24). The distinctive pupae of the parasitoid wasps may be readily found in the overwintering stem galls. They are slender, rounded on the anterior end and tapering to a point on the posterior end, with a shiny, thick, black exoskeleton, and they may appear to dangle from the inner wall of the gall, being attached to it at the posterior end by a short filament of unidentified material. The robust, black pupal exuviae are left behind in the stem like discarded leather jackets upon the emergence of the adult wasps.