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Nettle stem puparia

Nettle stem puparia
Roslien Woods, Winneshiek County, Iowa, USA
February 1, 2018
My goal in this post is to highlight some readily visible morphological differences between puparia I recovered from stinging nettle dead stalks, and to assert these differences correspond to two distinct types of puparia belonging to two different genera of agromyzids known to dwell in this microhabitat. Read on for the full story :)

Winter 2018 Fly puparia recovered from several overwintered dead stems of stinging nettle, Urtica dioica
Some of the adult agromyzids I reared from the stems I collected turned out to be Phytomyza flavicornis:

I also got some Melanagromyza adults from the stems...perhaps M. martini per

My written records aren't clear, but I am fairly sure that my specimens of Phytomyza flavicornis all emerged from the type of puparium shown on the right side of the current image: narrow, with a ribbed/scalloped (rather than smooth) profile, and with both posterior and anterior ends colored the same as the rest of the puparium.

In contrast, I believe the puparia on the left all belong to Melanagromyza. Note the smooth outline, and the black posterior horns that stand out strongly against the "straw" color of the rest of the puparium. These features are present on similar puparia (also Melanagromyza, I suspect) recovered from stem interiors of other host plants in my area:

Ex stem of Angelica atropurpurea (Apiaceae):

Ex stem of Arnoglossum plantagineum (Asteraceae):

If my hypothesis is correct, then the morphological differences shown in the current series can be used to help determine if a given puparium in a nettle stem belongs to Melanagromyza or to Phytomyza.

Images of this individual: tag all
Nettle stem puparia Nettle stem puparia - Melanagromyza Nettle stem puparia - Melanagromyza Nettle stem puparia - Phytomyza flavicornis Nettle stem puparia - Phytomyza flavicornis

Posterior morphology for immature stages of Melanagromyza
from (1)...

"The posterior spiracles of the larva and puparium [of Melanagromyza] consist of two sclerotized plates, each with an ellipse of pores or 'bulbs,' normally surrounding a conspicuous 'horn,' which is sometimes strongly sclerotized (fig. 127)." (p.18)

The authors even reference the larval posterior horns of Melanagromyza in their Key to Agromyzidae Subfamilies and Genera:
"...larval posterior spiracles on flat plate, with numerous bulbs, from 6 to 20, normally surrounding a strong black horn, the latter rarely atrophied to a mere scar (fig. 32)......Melanagromyza Hendel" (p. 15; emphasis added)

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