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Photo#1326699
Stem borer, big bluestem - Thrypticus

Stem borer, big bluestem - Thrypticus
Bald Spot Prairie, Winneshiek County, Iowa, USA
December 28, 2016
Borer in dead stem of big bluestem (Andropogon gerardii) in a small dry prairie remnant.

This dead stem showed signs of stem boring maybe 3 ft above the ground, but the larva was all the way down at the base of the stem only inches from the ground. Presumably it was responsible for the tunneling well above it on the stem, and had simply chewed its way down to where it was. What a life! Chew, chew, chew, down, down, down, slowly, methodically, meditatively even, in the dark.

After taking photos I returned this larva to its stem-home and will attempt to rear it to adulthood.

Adult reared from a larva with the same habit, same microhabitat, same site:

Images of this individual: tag all
Stem borer, big bluestem - Thrypticus Stem borer, prairie grass - Thrypticus Stem borer, prairie grass - Thrypticus Stem borer, prairie grass - Thrypticus Stem borer, prairie grass - Thrypticus

Moved
Moved from Insects.

Could be a Diptera, maybe an
Could be a Diptera, maybe an Agromyzidae? Just a guess

Moved
Moved from ID Request.

WSSF
This could be a larva of the wheat stem sawfly. I worked with them almost 10 years ago and I don't remember them being so yellow but it could be individual difference or because it is in another grass other than wheat. It exhibits this behavior though and would be found in your area. Do you know if it is a common pest in farms around you?

 
A sawfly?
Wow, I never would have guessed. How cool. Not much wheat around here to my knowledge, mostly corn and soybeans and hay/pasture (perhaps there is some wheat in the hay seed mixes?).

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