Midrib and petiole borer (Diptera: Agromyzidae) in Calystegia [0112]

OrderDiptera
FamilyAgromyzidae [P]
Lower taxonundetermined
No. spp. involvedOne confirmed [1-C]
Feeding modeMidrib and petiole borer
Host plantHedge bindweed, Calystegia sepium (Convolvulaceae)

Each larva of this borer appears to inhabit just a single leaf, tunneling out the interior of the petiole and sometimes part of the midrib as well. The walls of the tunnel have a noticeably ragged look to them. The leaf may wilt or shrivel and turn yellow or brown, betraying the presence of a larva at work in the leaf stalk. Some larvae prepare an exit shaft to near the surface of the petiole and pupate there, leaving the epidermis intact except for penetrating it with the anterior spiracles. The finding in 2022 of other petioles with completed tunnels but no culprits present suggested that these leaves' larvae had exited the petioles and pupated externally, but this was not confirmed. An effort to rear adults from overwintered puparia in 2022-2023 was unsuccessful.

IMG#: 0112-13
Host plant vine, with a single leaf that has noticeably yellowed, indicating the presence of a borer in the leaf midrib and petiole. (Photo date: July 9, 2022)
IMG#: 0112-01
Portion of hedge bindweed vine with a leaf that has shriveled and turned brown, indicating the presence of a borer in the leaf midrib and petiole. (Photo date: July 10, 2022)
IMG#: 0112-02
Closeup of an affected leaf.
IMG#: 0112-14
An affected petiole, backlit, showing internal discoloration resulting from the tunneling in the petiole interior.
IMG#: 0112-03
An affected petiole, still attached to the main stem. Note the discoloration of the petiole, and the exit window in the petiole at lower left with the puparium's anterior spiracles projecting.
IMG#: 0112-04
Another view of the petiole from the previous photo (0112-03).
IMG#: 0112-05
Lower portion of affected petiole, with the fly's as-yet unused exit window visible. Also note the abcission point where the petiole is beginning to detach from the main stem -- presumably a result of the plant shedding it because it was damaged by the borer inside.
IMG#: 0112-06
Base of affected petiole, showing exit window with anterior spiracles of puparium projecting.
IMG#: 0112-07
Exit window in petiole, with anterior spiracles of puparium projecting.
IMG#: 0112-08
Anterior spiracles of puparium projecting through exit window.
IMG#: 0112-09
Interior of affected petiole, showing ragged tunnel walls.
IMG#: 0112-10
Affected petiole, dissected, showing puparium inside.
IMG#: 0112-11
Posterior of puparium, showing rear spiracles.
IMG#: 0112-12
Anterior spiracles of puparium.
IMG#: 0112-15
Interior of another affected petiole, showing tunnel with ragged walls.

Specimen data for images

Field photo taken 07/09/22 (13); coll. 07/09/22, photos taken 07/10/22 (01-12, 14-15).

All specimens above from the Upper Midwest, USA.

References

[none]

Page created 09/08/23. Last update: 07/06/24