Stem borer (Lepidoptera: Tortricidae) in Arnoglossum

Record Details

Record no.:	0077
Feeding guild:	Stem borer
Taxonomy:	Lepidoptera: Tortricidae: cf. Cochylini
Stages observed:	trace, larva, pupa, adult
Hosts in Arnoglossum:	A. ?reniforme (woodland indian-plantain)

I discovered a dead larva in its tunnel in an upper stem, along with several cocoons with live pupae inside, in the interiors of dead stems of the host in late winter. The larva possessed a shiny black head capsule and thoracic shield along with a scattering of long setae on the body segments. Pith damage in the inhabited stems indicated that larvae had tunneled in the upper stems or excavated the pith lining the inner walls of lower stems. The cocoons were oval and somewhat flattened, formed of silk covered in a neatly arranged layer of yellowish-brown frass, and they opened into an exit flap formed in the epidermis of the stem. The pupa was thrust through the exit flap upon the adult's emergence in spring. Adults, reared in 2023, have not yet been identified beyond family level.

Featured Images

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tunnel in brown pith of stem, with irregular walls, scattered pellets of dry frass, and a shriveled caterpillar carcass in the middle — Image #: 77-01 Larva (deceased) in dead stem of host. (Photo date: April 14, 2023)

the body of the caterpillar has contracted to be about 4.5 times as long as wide and it is tucked inside the stem tunnel — Image #: 77-02 Larva (deceased) in dead stem of host.

the larva's brown body is wrinkled at the location of the boundaries between the thoracic and abdominal segments, and the body features scattered long setae along with a shiny black head capsule and prothoracic shield — Image #: 77-03 Larva (deceased) from dead stem of host, lateral (top panel) and dorsal (bottom panel) views.

lower in the same stem, the pith has been mostly consumed and the tunnel walls are smoother; dry brown pellets of frass are scattered here and there — Image #: 77-04 Feeding damage and frass in stem interior.

the exterior of the dead stem is brown and ridged, featuring a single small cut made in a semicircle shape with one end of the semicircle extended briefly into a straight line; the flap created by this slit is still flush with the rest of the stem wall — Image #: 77-05 Exterior of dead stem of host, showing semicircular cut made from the inside by the larva prior to pupation as part of the larva's effort to establish an exit window for the adult-to-be. The insect's still-occupied, frass-covered cocoon is inside the stem at this location, with a silk collar that opens into the as-yet unusued exit window. (Photo date: April 14, 2023)

the flap created by the semicircular cut has rough edges, apparently due to the way it was cut by the larva's mandibles — Image #: 77-06 Detail, exit window that includes a semicircular cut in the outermost layer of stem tissue. (larger version)

cocoon is 3.5-4 times as long as wide, tapered on the ends and covered in a layer of neatly arranged, light brown pellets of dry frass — Image #: 77-07 Cocoon inside the stem at the location of the exit window from the previous photos (0077-05 and 0077-06). (larger version)

the exit hole is roughly circular and the outer wall of the stem has been partly broken away adjacent to the hole, revealing the neck of the cocoon curving to the hole — Image #: 77-08 A second inhabited stem, dissected, showing cocoon and silk collar forming tunnel to exterior. The tunnel was covered by a thin strip of stem epidermis (an exit window) before the stem was dissected for this photo. The insect is still inside its cocoon.

the neck of the cocoon is more or less smooth inside and has been cut at an angle for the photograph, creating an oval cross-section — Image #: 77-09 Cocoon with tunnel leading to stem exterior.

brown papery exuviae with a split open anterior end projecting into the air and the posterior end still buried in the stem interior — Image #: 77-13 Pupal exuviae protruding from stem after adult's emergence. (Photo date: April 27, 2023)

the same scene as image 13 except viewed from the stem interior, showing the lower part of the pupal skin emerging from the neck of the cocoon — Image #: 77-14 Affected stem, dissected after adult's emergence, showing pupal exuviae protruding from cocoon through the wall of the stem. (larger version)

the anterior end of the caramel-colored exuviae is rounded and there is a wedge-shaped slit where the exuviae split open to allow the adult moth to emerge — Image #: 77-15 Pupal exuviae after adult's emergence. (larger version)

the moth is roughly triangular in shape; the posterior part of the folded wing is broader and formed into an arch, and there is a tuft of featherlike scales on the dorsal surface of the thorax — Image #: 77-10 Reared adult, lateral. (larger version) (Photo date: April 24, 2023)

the moth's plumage is multicolored in shades of dark red, white, brown, and gray, with a large circular yellowish-brown patch bordered by a small triangular black patch on the rear part of the folded forewing — Image #: 77-11 Reared adult, lateral. (larger version)

viewed from this angle the moth's body is narrow and streamlined as it rests on the gray substrate — Image #: 77-12 Reared adult, dorsal.

Specimen Data for Images

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Coll. 04/12/23, photos of dead larva and stem damage and cocoons on 04/14/23 (01-09), adults em. 04/23/23-04/26/23, photos of adult on 04/24/23 (10-12), photos of pupal exuviae on 04/27/23 (13-15).

Page created: November 13, 2023. Last update: February 7, 2026