Stem borer (Diptera: Agromyzidae) in Apios

Record Details

Record no.:	0062
Feeding guild:	Stem borer
Taxonomy:	Diptera: Agromyzidae
Stages observed:	trace, larva, puparium, adult
Hosts in Apios:	A. americana (groundnut)

My initial observations of this fly occurred in 2021 and 2022. The larva tunnels in the stem interior of the host. It shows a conspicuous hooklike process in front, probably a rather enlarged mouthhook but further study is needed. The bulbs of the posterior spiracles are arranged palmately in a projecting, three-dimensional semicircular fan, a rather exceptional configuration among the dozens of stem-boring Agromyzidae I have studied in this survey.

The puparium is unusually narrow for its length, dome-shaped anteriorly and tapering noticeably to the posterior. Its curious shape is similar to that of the agromyzid borer in Desmodium (record 0192, 0194), which host is, interestingly, also in the Fabaceae. The puparium overwinters, and adults emerge in spring.

Adults are black overall, lacking appreciable iridescence on the abdomen. They show some limited brownish coloration on the lateral surface of the thorax near where the wing attaches. The haltere has a black knob and a brown stem.

Featured Images

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green stem with tunnel through middle of airy pith — Image #: 62-01 Tunnel in stem of host. (Photo date: August 13, 2021)

yellow elongate larva with posterior end held above pith — Image #: 62-02 Larva, partly extricated from dissected stem.

the side of the larva is pale yellow and shiny and the short paired brown knobs on the rear end are the posterior spiracles — Image #: 62-03 Posterior of larva.

larva is about eight times as long as wide, the body smooth but slightly ribbed at segment boundaries — Image #: 62-04 Lateral view of larva removed from stem.

long black hooked mouthpart on the tapered front end of the larva — Image #: 62-21 Hooklike structure on front of larva -- evidently a much enlarged mouthhook.

the spiracles are pale knobs each having 14-18 reddish bulbs arranged in a fan — Image #: 62-05 Views of posterior spiracles of larva.

ribbed yellow puparium is shaped like a pill and embedded in rough-textured brown pith — Image #: 62-06 Puparium overwintering in dead stem. (Photo date: January 15, 2022)

yellow puparium, narrow and cylindrical with a domed, slightly pointed front end — Image #: 62-07 Overwintering puparium.

puparium is about five times as long as wide with brown segment lines, the body tapering to the posterior, on a gray background — Image #: 62-08 Puparium, lateral, with millimeter ruler for scale.

the brown color on the rounded front end of the puparium and the ridged texture of the puparium body are prominent here — Image #: 62-09 Additional views of puparium.

detail of dome-shaped front end of puparium, showing variegated brown and yellow rough texture with two tiny reddish knobs (spiracles) at the tip — Image #: 62-10 Anterior spiracles of puparium.

the spiracle is cone-shaped with a bulblike end, not unlike a football trophy — Image #: 62-11 Another view of anterior spiracles of puparium.

each spiracle is reddish with bulbs splayed outwards like tiny short fingers or impact ejecta — Image #: 62-12 Posterior spiracles of puparium.

in this rear view the spiracle bulbs are arranged in a long arc, about 315 degrees total — Image #: 62-13 Posterior spiracles of puparium.

light shines through the semi-translucent puparium highlighting the wing pads and neatly folded legs and red compound eyes of the pupa inside — Image #: 62-14 Overwintered puparium, after being held at room temperature indoors for a few weeks, showing pupa maturing inside.

on the pupa inside, the wing pads and legs are black, the abdomen is pale yellow — Image #: 62-15 Overwintered puparium, after being held at room temperature indoors for a few weeks, showing pupa maturing inside.

fly with huge red compound eye and black body — Image #: 62-16 Reared adult, lateral.

the black stocky thorax and slender abdomen of the fly are somewhat dull but also somewhat reflective with a brighter sheen on the side of the abdomen — Image #: 62-17 Reared adult. lateral.

triangular wings are folded back at an angle, thorax is smooth and rounded, head is dome shaped with prominent eyes — Image #: 62-18 Reared adult, dorsal.

wings held above body, showing their transparency with a slight rainbow sheen — Image #: 62-19 Reared adult, dorsolateral.

the black veins of the wing converge towards the base of the wing and some specks of pale dirt stand out on the fly's head and thorax — Image #: 62-20 Reared adult, dorsal.

Specimen Data for Images

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Coll. 08/11/21, photos on 08/13/21 (01-05 and 21); coll. 01/13/22, photos on 01/15/22 (06-13) and 03/21/22 (14-15); coll. 01/13/22, adults em. 03/26/22 (16-18) and 03/21/22 (19-20).

Page created: September 17, 2023. Last update: February 1, 2026