Local feeder (Diptera) in stems of Festuca

This Diptera larva (cf. Cecidomyiidae) shared a Festuca subverticillata culm internode with a larva of Thrypticus (Diptera: Dolichopodidae, record 0812). It was positioned near a patch of black fungal tissue on the inner wall of the culm, a few centimeters above the Thrypticus larva. The hollow space within this stretch of culm had also filled loosely with what appeared to be whitish fungal hyphae.

I found the two larvae sharing the culm on 23 August 2026. By 31 August, the ?cecidomyiid larva, which I was keeping in a rearing container, had crawled off the sectioned culm piece and onto the wall of the rearing container, where it spun an elongate, white cocoon.

Information about this larva and its Thrypticus associate is also available at Host associations, feeding traces, larval morphology, and other observations on the life histories of culm borer flies in the genus Thrypticus (Diptera: Dolichopodidae) from the Upper Midwest, USA.