04-12-14 Botany Field Note

04-12-14 Botany Field Note

April 12, 2014

Marirose Kuhlman's Botany Field Note details insect induced big sagebrush galls, sagebrush buttercups, and yellowbells.

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Botany Field Note April 2014 Marirose Kuhlman

Forty-two species of herbivorous gall-inducing insects rely on big sagebrush (Artemesia tridentata) to complete their life cycles. A Cecidomyiid gall midge (Rhopalomyia spp.) likely caused the galls on the sagebrush plant pictured below. Rhopalomyia gall midges occur throughout the range of big sagebrush and induce gall formation on all three of its subspecies. Adult Rhopalomyia females lay eggs on sagebrush plants in spring, galls form around feeding larvae in late summer, and larvae overwinter inside. Pupae emerge from galls in the spring and the cycle begins again.

Variation in gall morphology identifies the insect species within the gall. These photos show two examples of sagebrush gall variation found at a single site.

A rust fungus (Puccinia monoica) infects these rockcresses (Arabis holboellii) above and causes the plants to create “pseudoflowers.” Fungal hyphae produce the yellow color and a sticky, sugary substance on the leaves, mimicking spring co-blooming species such as buttercups (Ranunculus glaberrimus) and yellowbells (Fritillaria pudica). This floral mimic must outcross and relies on insect visitation to complete sexual reproduction. The photos below show healthy, uninfected rockcresses.

Yellow color produced by the Puccinia monoica fungus on rockcress is indistinguishable in the visible and ultraviolet spectra from that of buttercups, such as this sagebrush buttercup (Ranunculus glaberrimus) pictured above. Yellowbells (Fritillaria pudica – right) and buttercups must share and compete for their insect pollinators with the Puccinia monoica rust fungus.

A mourning cloak butterfly (Nymphalis antiopa) finds nutrients in snow melt. Spring-flying mourning cloaks emerged as adult butterflies last summer and hibernated as adults over the winter. They occur in every U.S. state except Hawaii and are Montana’s State Butterfly. Diminuitive bulbous woodland star (Lithophragma glabrum - left) graces the sagebrush steppe. References: Hufbauer, R.A. (2004). Observations of sagebrush gall morphology and emergence of Rhopalomyia pomum (Diptera: Cecidomyiidae) and its parasitoids. Western North American Naturalist 64(3):324-330. Roy, B.A. (1993). Floral mimicry by a plant pathogen. Nature 362:56–58 Welch, B.L. (2005). Big sagebrush: A sea fragmented into lakes, puddles, and ponds. General Technical Report. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fort Collins, CO.

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