The latest issue of Cicindela (a quarterly journal devoted to tiger beetles), which arrived in my mailbox last week, features an article coauthored by my good friends Kent Fothergill and Kelly Tindall of Portageville, Missouri, along with lead author Stephen Bouffard of Boise, Idaho (Bouffard et al. 2009). The article reports the results of a vegetative management pilot test for using herbicides to restore habitat for the critically imperiled St. Anthony dune tiger beetle, Cicindela arenicola. This species is endemic to Idaho, primarily the St. Anthony Dunes area in the southwestern part of the state (Pearson et al. 2006), and like the Coral Pink Sand Dunes tiger beetle (Cicindela albissima, recently covered in this post) it is restricted to sand dune habitats that are threatened by a variety of land-use practices, including motorized vehicle use, livestock trampling, intentional stabilization of dunes by grass seeding, conversion of dune habitats to agriculture, and disposal of public lands by transfer to private ownership (Idaho State Conservation Effort 1996).
Bouffard et al. conducted their study at Minidoka National Wildlife Refuge in southern Idaho. Cicindela arenicola was recorded on small remnant sand dunes within the refuge during the mid-1990’s but had not been detected in more recent opportunistic searches. The authors noted that the sand dunes appeared to have become overgrown with the invasive annual grass, downy brome (Bromus tectorum). Their study comprised three elements: 1) herbicide treatment on dune habitats to reduce downy brome density; 2) surveys of treated versus untreated plots during the following season to assess the efficacy of the herbicide in reducing downy brome density and any effect it might have on native vegetation, as well as the presence of C. arenicola; and 3) laboratory bioassays to evaluate the acute toxicity of herbicides on a surrogate tiger beetle species, Cicindela repanda (common shore tiger beetle). The laboratory bioassays were necessary, because toxic effects by a herbicide against tiger beetles would negate its potential usefulness for habitat improvement. For the herbicide treatment plots, Imazapic (trade name Plateau®) was selected because of its effectiveness against downy brome, minimal effects on native vegetation, and low toxicity to animals, including insects. Imazapic is labeled for control of downy brome and for use on rangeland. A nonselective herbicide, glyphosate (trade name Touchdown®) was also evaluated in the laboratory bioassay, even though it was not used in the field test, because glyphosate-based herbicides also have low animal toxicity and have been shown to be effective in assisting the establishment of native plant species in prairie restorations.
The authors were successful in observing live adult C. arenicola in both of the test plots where adults of this species were last seen in the mid-1990s. Moreover, larval burrows – putatively representing this species – were also noted in the plots. No adults or larvae were seen in a third plot; however, no previous records of the species exist in the area where that plot was located. They noted the presence of residual downy brome stems from the previous season’s treatment in the sprayed plots but no new growth, while the untreated controls exhibited extensive new downy brome growth. More importantly, no negative impacts on native vegetation – principally rabbitbrush (Chrysothamnus sp.) and Indian ricegrass (Achnatherum hymenoides) – were noted in the sprayed plots. The third plot had only a light downy brome invasion prior to treatment, and no apparent negative effects were observed on the native bunchgrasses, rabbitbrush, and sagebrush (Artemisia tridentata) in this plot after treatment. In the laboratory, neither imazapic nor glyphosate showed evidence of acute toxicity against the surrogate tiger beetle, C. repanda.
While the use of herbicides for conserving endangered species may seem counterintuitive, this study demonstrates a potential use for herbicides in restoring and improving sand dune habitat for a critically imperiled species of tiger beetle. Herbicides that are effective in reducing invasive annual grasses with minimal effects on both native vegetation and tiger beetles could greatly facilitate habitat management for a number of critically imperiled western U.S. sand dune tiger beetles besides C. arenicola, including C. albissima in southwestern Utah, C. waynei (Bruneau tiger beetle) in western Idaho, and C. theatina (Colorado Great Sand Dunes tiger beetle) in southern Colorado. Where vegetational encroachment presents a threat to critical sand dune habitat, broad spectrum or grass selective herbicides may offer an effective and convenient alternative to habitat restoration. Additional research will be needed to determine if repeat applications of herbicides will be necessary to prevent reinvasion, and if so with what frequency, as well as the chronic or behavioral effects of herbicides on both larval and adult forms of the insects targeted for conservation.
I thank Kent Fothergill for allowing me to use his beautiful field photograph of C. arenicola, which also graces the cover of the current issue of Cicindela.
Bouffard, S. H., K. V. Tindall and K. Fothergill. 2009. Herbicide treatment to restore St. Anthony tiger beetle habitat: a pilot study. Cicindela 41(1):13-24.
Idaho State Conservation Effort. 1996. Habitat conservation assessment and conservation strategy for the Idaho Dunes Tiger Beetle. Report No. 7, Boise, ID.
Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.
Copyright © Ted C. MacRae 2009