Stem borer (Diptera: Agromyzidae) in Lapsana

Record Details

Record no.:	0306
Feeding guild:	Stem borer
Taxonomy:	Diptera: Agromyzidae: Melanagromyza sp.
Stages observed:	trace, puparium
Hosts in Lapsana:	L. communis (nipplewort)

The larva tunnels in the layer of pith lining the interior of the hollow stem. Pupation occurs in the pith, with an exit window prepared nearby in the outer wall of the stem, and in at least some cases the puparium is evidently the overwintering stage. The insect is tentatively identified as Melanagromyza sp. based on the color, shape, location, and posterior spiracles of the puparium.

Featured Images

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result of larva's tunneling in stem — Image #: 306-01 Dead stem of host, split open lengthwise, showing raised "molehill" tunnel in pith, running from left to right along the horizontal center line of the image, and ending in a rounded dead-end not far from the right edge of the frame. A second length of tunnel in the pith, created by the same larva, was breached when the stem was split open, exposing the ragged interior of the tunnel; this length of tunnel runs across the entire frame, above the horizontal center line of the image. (Photo date: November 6, 2022)

the larva finished tunneling here and pupated — Image #: 306-02 Stem interior, with a small amount of pith scraped away, revealing puparium in "molehill" tunnel in pith.

the adult fly will emerge from the exit window after vacating the puparium — Image #: 306-03 More pith removed, revealing tunnel with puparium inside, along with the exit window in the far wall of the stem. (Photo date: November 6, 2022)

light shines through the backlit exit window in the split-open stem with the puparium resting just behind the window in the larva's tunnel — Image #: 306-04 Tunnel with puparium and exit window.

a few shreddings from larval feeding / excavation are clumped near the puparium — Image #: 306-05 Detail, puparium in tunnel with exit window nearby.

the exit window is oval, about twice as long as wide, and translucent — Image #: 306-06 As-yet unused exit window, viewed from the stem interior.

the split-open stem is backlit so that the exit window is brighter than the surrounding tissue — Image #: 306-07 As-yet unused exit window, viewed from the exterior of the stem.

the oval shape of the window is somewhat flattened, almost approaching rectangular — Image #: 306-08 Exit window, viewed from the exterior of the stem.

the tunnels lift up the inner surface of the pith lining since they are slightly wider in diameter than the pith lining is thick — Image #: 306-09 Cross section of affected stem, showing tunnels in the layer of pith lining the hollow stem interior.

yellow pupa stage with faint banding from body segments — Image #: 306-10 Puparium. (Photo date: November 6, 2022)

the horns are useful for narrowing down identification possibilities — Image #: 306-11 Lateral view, posterior spiracles of puparium, showing strong curved horns.

the horns are long, black, and hooked — Image #: 306-12 Posterior spiracles of puparium.

Specimen Data for Images

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Coll. 11/06/22, photos same day (01-12).

Page created: January 6, 2024. Last update: February 2, 2026