Stem borer (Lepidoptera: Tortricidae) in Scrophularia [0499]

Order	Lepidoptera
Family	Tortricidae[M,L,P,A]
Lower taxon	Endothenia cf. hebesana
No. spp. involved	One confirmed [1-C]
Feeding mode	Stem borer
Host plant	Figwort, Scrophularia sp. (Scrophulariaceae)

Later-stage larvae of this tortricid feed in the stems of the host, excavating galleries and expelling frass (or sometimes retaining it in the tunnels). They overwinter in the stems and emerge as adults in spring -- that is, if they manage to avoid winter predation by birds who seem to have caught on to this plant-insect association in the geographic area covered by the current study. In fact, it was the birds' holes pecked in figwort stems as they hunted Endothenia larvae that first clued the author in to the presence of this borer inside the stems.

Early-instar larvae may feed in the fruits of the host before proceeding to the stems; this is documented in the images below along with the stem feeding.

The species identity is not yet known for certain, but E. hebesana has previously been recorded from Scrophularia (Barnd et al. 2020).

IMG#: 0499-18
Fruits of figwort, *Scrophularia* sp., at a time in which some are inhabited by early-instar *Endothenia* larvae. Fruit-feeding larvae may later go on to tunnel in stems (see images below). (Photo date: August 23, 2021)

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IMG#: 0499-14
Figwort fruits, after being held for several days indoors, showing frass accumulation due to larvae tunneling inside. This may sometimes be the precursor feeding stage to stem tunneling for this lepidopteran. (Photo date: August 26, 2023)

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IMG#: 0499-15
Affected fruit. Note that some of the outermost layers of fruit tissue have been scraped away around the perimeter of the entrance hole. This characteristic is also shown in the species' entrance holes in the stem (see images 0499-01 and 0499-18, below).

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IMG#: 0499-17
After feeding in fruits, larvae may move on to tunneling in stems (and some larvae may begin in stems without feeding on fruit at all, although this is speculative). This late-season stem has been heavily tunneled around a node, resulting in large quantities of frass being expelled from one or more hidden holes in the wall of the stem. Also note the scraping away of outermost layers of tissue in the vacinity of the hidden holes, similar to what was done to the fruits in images 0499-14 through 0499-16 (above). (Photo date: September 29, 2023)

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IMG#: 0499-01
*Endothenia* entrance hole in figwort stem. Note the partial excavation of outer layers of tissue around the perimeter of the hole, similar to the damage done to fruits in images 0499-14 through 0499-16 (above).

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IMG#: 0499-02
Figwort stem, dissected, showing entrance hole (at right), tunnel filled with frass (at center), and larva partly concealed within silk webbing (at left).

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IMG#: 0499-03
Two larvae, posed side by side in their respective stems.

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IMG#: 0499-06
Anterior end of larva, dorsal.

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IMG#: 0499-07
Pupal exuviae protruding from stem after adult's emergence in captivity. (Photo date: May 25, 2016)

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IMG#: 0499-10
Affected stem, attacked by a bird for the larvae within, resulting in irregular holes in the stem with a "broken-into" appearance (the stem has been broken into by a bird's bill, as opposed to chewed open by a caterpillar; compare these bird holes to the caterpillar-chewed entrance hole in image 0499-01 above). (Photo date: April 10, 2016)

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IMG#: 0499-11
More figwort stem holes punched by a bird attempting to collect *Endothenia* larvae. (Photo date: April 10, 2016)

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IMG#: 0499-12
More figwort stem holes punched by a bird attempting to collect *Endothenia* larvae. (Photo date: April 10, 2016)

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IMG#: 0499-13
This dead stem of figwort contains eight holes created by animals seeking to gain entry. Seven were made by a bird, and one was made by a caterpillar. Using the information provided on this page, can you identify the caterpillar-created hole? (Click here for a larger version of the image.)

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Specimen data for images

Coll. 01/01/17, photos on 02/05/17 (01-02, scraped stem entrance and larva in tunnel inside); coll. 10/18/16, photos same day (03-06, reddish-purple larvae in stems); coll. as larva in stem on 02/05/16, em. 05/24/16 (07-09, adult and pupal exuviae); field photos on 04/10/16 (10-12, bird-attacked stems in the field); coll. winter ?2016, photo on 07/27/22 (13, bird-attacked stem); coll. 08/23/21, field photo same day (18, fruit), additional photos 08/26/21 (14-16, tunneled fruit w/ larva); field photo on 09/29/23 (17, heavily tunneled stem with extensive frass accumulation on exterior).

References

Barnd, B., Thomas, A.W., Zimlich, R.L., O'Connor, M., and R. Hardy. 2020. Species Endothenia hebesana - Verbena Bud Moth - Hodges#2738. Species page on BugGuide.net. Retrieved October 2, 2023 from https://bugguide.net/node/view/132143.

Page created 10/02/23. Last update: 11/19/24