Stem borer (Diptera: Agromyzidae) in Arnoglossum

Record Details

Record no.:	0075, 0078
Feeding guild:	Stem borer
Taxonomy:	Diptera: Agromyzidae: Melanagromyza arnoglossi
Stages observed:	trace, larva, puparium, adult
Hosts in Arnoglossum:	A. plantagineum (prairie indian-plantain); A. reniforme (great indian-plantain)

I found puparia and a larva in stems of A. reniforme and A. plantagineum, with one or more adults reared from both hosts. In A. reniforme the larval tunnels were formed in the pithy inner lining of the hollow stems, while in A. plantagineum the relatively solid pith was riddled with the tunnels of several larvae per stem. Puparia from both hosts possess fairly strong black horns on the black posterior spiracular plates. It appears that the puparium is the typical overwintering stage. M. arnoglossi was described in Eiseman et al. (2021) using adults reared from A. reniforme.

A probable Melanagromyza that I believe to be a different species than M. arnoglossi tunnels in basal leaf petioles of A. reniforme in my study area (record 0686). The anterior and posterior spiracles of its puparium are noticeably different from those of M. arnoglossi.

Featured Images

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the long slender piece of stem is concave inside with a thin lining of whitish pith, and a narrow tunnel winds through the pith layer from one end of the frame to the other — Image #: 75-01 Tunnel in pith of *A. reniforme*.

this image is similar to the previous one except there are now four pieces of affected stem in the frame, each with a tunnel winding in a different trajectory through the pith — Image #: 75-02 Stem interiors of several pieces of *A. reniforme* stems, showing tunnels in pith.

the puparium is straw-colored and partly buried in the pith; subtle transverse bands are visible at the boundaries between body segments of the puparium — Image #: 75-03 Puparium in end of stem tunnel, *A. reniforme*.

the puparium tapers to a rounded point on either end; the posterior spiracle hooks protrude from the rear end and a circular anal scar is evident just in front of the posterior spiracles in the ventral view — Image #: 75-04 Puparium from stem of *A. reniforme*, in dorsal (left panel), ventral (middle panel), and lateral (right panel) views.

what remains of the pithy stem interior is riddled with crisscrossing tunnels and at least five spent puparia are scattered in the tunnels — Image #: 75-05 Stem of *A. plantagineum* heavily tunneled by at least five larvae.

the pill-shaped puparia have their front ends split open or broken off, indicating successful emergence of the adult flies — Image #: 75-06 Spent puparia in *A. plantagineum* stem.

the larva is cylindrical and yellow, about six times as long as wide, and the front end tapers to a point with the black mouthhooks crowning the point — Image #: 75-07 Lateral view, larva from *A. plantagineum* stem.

the posterior spiracular hooks point upward, the mouthhooks and head skeleton are hidden under the soft tissues of the larva's front end, and the anterior spiracles form two small dots set back a short distance from the tapered front end — Image #: 75-08 Dorsal view, larva from *A. plantagineum* stem.

the two puparia are shaped similarly; both feature a reddish-orange scar at the location of the mouth opening of the final-instar larva, a similarly colored round anal scar near the rear of the puparium, and hooked posterior spiracles — Image #: 75-09 Comparison of puparia from stems of *Arnoglossum reniforme* (left panel) and *A. plantagineum* (right panel). Ventral views shown.

in the puparium from A. reniforme the spiracular hooks are somewhat more curved and the spiracle plates touch each other, while in the larva and puparium from A. plantagineum the spiracular hooks are straighter and the spiracle plates are separated by about half their width — Image #: 75-10 Comparison of posterior spiracles of puparium from stem of *Arnoglossum reniforme* (left two panels) and larva and puparium from stem of *A. plantagineum* (right two panels).

each black spiracle plate is shaped like a half-circle and the two half-circles are appressed to one another with the hooks in the middle and the tiny bulbs ringing the outside — Image #: 75-11 Rear view of posterior spiracles of puparium from *A. reniforme* stem; note curved upturned hooks, and spiracle bulbs arranged in an arc along the outside edge of the spiracle plates.

References

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Eiseman, C.S., Lonsdale, O., van der Linden, J., Feldman, T.S., and M.W. Palmer. 2021. Thirteen new species of Agromyzidae (Diptera) from the United States, with new host and distribution records for 32 additional species. Zootaxa 4931(1): 1–68.[return to in-text citation]

Page created: February 10, 2026. Last update: February 11, 2026