Managing rare plants in the Bureau of Land Management includes understanding plant-pollinator relationships. This article highlights the U.S. Department of Interior role in and commitment to pollinator conservation.  Without pollinators, humans and ecosystems cannot survive. June 24-30, 2007, has been designated National Pollinator Week by the U.S. Senate (S. Res. 580) and the U.S. Department of Agriculture. Find out what’s happening during National Pollinator Week in your area or post your event at www.pollinator.org.

How important are insects in Southwestern Idaho? That question is always on the mind of Dr. Ian Robertson, an associate professor of biology at Boise State University.  Robertson, an entomologist who studies insect-mediated pollination, herbivory and seed predation by insects, as well as host choice decisions in bark beetles, is partnering with the Bureau of Land Management, Idaho State Office, to determine the importance of insect pollinators to slickspot peppergrass, Lepidium papilliferum, a rare type of mustard endemic to southwest Idaho.

A recent report released by the National Academy of Sciences on the status of pollinators in North America recommended that federal land-management agencies increase their efforts to understand pollinator needs and reverse habitat decline.  One of the specific recommendations of the report — to establish discovery surveys for pollinators of rare, threatened and endangered plants — is of interest to Robertson, who has been studying insects associated with slickspot peppergrass for several years.
 
Slickspot peppergrass is a species of conservation concern. Within a small range of sagebrush-steppe habitat in southwestern Idaho, the plant is restricted to growing in “slick spots,” bare, shallow depressions that are high in clay content and where water accumulates when it is available. Several recent studies show that many populations of the plant are declining within its very small geographic range. The plant was recently considered for inclusion on the list of species protected by the Endangered Species Act and is now managed through a Conservation Agreement with the USFWS, agencies in the state of Idaho, BLM and the Department of Defense. 

Robertson’s investigations show that slick spot peppergrass relies on pollination by insect visitors for fruit and seed production. In the absence of insects the plants can self-pollinate, but only to a very limited extent with little seed production. Insects are clearly needed for the plant to reach its full reproductive potential, thus insect pollinators to the rescue!

Which insects pollinate slickspot peppergrass? Dr. Robertson continues to monitor plants and conduct experiments to answer this question.  He and his graduate students have found that insects from as many as 25 families visit slickspot peppergrass flowers, but the most prominent pollinators include a number of wasp species (e.g., mud daubers, thread-wasted wasps); bees (e.g., sweat bees, honeybees, carpenter bees); and flies (e.g., tachinid flies and bee flies).

Many of the other insect visitors also serve as pollinators but to a lesser extent. Some, like chrysomelid beetles, are not pollinators at all — they eat flower petals; and harvester ants abscond with fruits and seeds late in the season so they aren’t available to replenish slick-spot peppergrass populations.

Despite the wealth of knowledge obtained over the last several years about the relationships between insects and slickspot peppergrass, much more remains to be discovered. Future research questions of interest to both the BLM and Robertson include:

• determining the relative importance of specific pollinators on reproduction in slickspot peppergrass;

• determining the effects of surface disturbance on ground-dwelling predators in sagebrush habitats;

• documenting changes (if any) in pollinator abundance across years,

• determining the importance of crab spider predation on insects that visit slickspot peppergrass flowers;

• quantifying the impact of seed predation by harvester ants on slickspot peppergrass recruitment; and

• clarifying the role insect pollination plays on the genetic structure of slickspot peppergrass populations.

For additional information, contact Roger Rosentreter at (208) 373-3824; Roger_Rosentreter@blm.gov