Cecidomyiidae

Rhopalomyia

Artemisia tridentata

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Rhopalomyia tumidicaulis

This species and R. hirticaulis form the only stem galls known on A. tridentata. 

Adults emerged September 19-25, 1968 from galls collected on September 4 with pupae present. 

This polythalamous gall (Fig. 42) reaches maturity in the early fall just prior to bloom. It forms a swelling on a vegetative stem that becomes stunted, has numerous nodes and has small malformed leaves. Interspersed among the wood fibers of the inner stem are the sclerenchymatous larval capsules. 

The length of nine of these stunted stems ranged from 5-23 mm (avg. 15). Three galls contained six, seven and eight larval capsules respectively.  

Biology and taxonomy of the Rhopalomyia Gall Midges (Diptera: Cecidomyiidae) of Artemisia tridentata Nuttall (Compositae) in Idaho

The integral, polythalamous stem galls of this midge develop on new growth of Great Basin sagebrush in summer, reaching maturity in early fall. 

Plant Galls of the Western United States