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‘Chem herding’ to improve biological control of saltcedar (Tamarix spp.) in the Northern Rockies

Date: August 08, 2019

An aggregation pheromone used by the northern tamarisk beetle Diorhabda carinulata to locate members of the same species is essential for colonization and reproductive success


The photo shows a plastic, yellow cattle ear tag with a wire cage around it hanging from a tree. There are five round objects inside the cage that are the lure.
Diorhabda carinulata aggregation pheromone based lure on cattle ear tag inside wire mesh cage.

Background

Saltcedar (Tamarix spp.) refers to the complex of exotic invasive shrubs and trees (four species and their hybrids) now considered the third most prevalent woody riparian taxonomic group in the western United States. Defoliation by large multivoltine populations of the Northern tamarisk beetle Diorhabda carinulata has successfully reduced extensive saltcedar infestations in the southwestern United States. Behavioral manipulation of insects with semiochemicals such as aggregation pheromones can be used to intensify herbivory, even in the Northern Rockies where beetle population densities are inherently low, to the extent that the target weed species is negatively affected at a population level.

Research

Diorhabda carinulata may rapidly disperse from release sites, particularly when densities are too low to produce adequate aggregation pheromone to retain reproductive adult beetles onsite. This can result in the loss of fitness due to small effective population size (Allee effects). Releases of 5,000 adults are recommended to ensure establishment. Interstate movement of Diorhabda spp. has been prohibited since the 2005 listing of Tamarix spp. as critical nesting habitat for the southwestern willow flycatcher (Empidonax traillii extimus), even to areas well outside of the range of this federally protected avian species. Lures impregnated with aggregation pheromone were initially tested in Wyoming on established but sparse populations of D. carinulata. Releases of 200-1,000 D. carinulata were subsequently made at a number of sites in eastern Montana where the agent had not yet established. Released beetles originated from a continuous laboratory colony initiated from a small number of individuals field collected in south central Montana. This study evaluated the potential role of semiochemicals for spatial manipulation of herbivorous insect species, specifically to direct or guide colonization, and facilitate aggregation of small density releases. Application of this concept to classical weed biological control intensified herbivory on target weeds and increased agent efficacy.

The photo shows a technician hanging up a pheromone lure on a bush.
Applying pheromone lure in stable wax-based matrix to caged cattle ear tag.

Key findings

  • Operational deployment of aggregation pheromone based lures in an environmentally stable, controlled release formulation allowed for the successful delivery of behaviorally active semiochemicals at a consistent rate over an extended period of time.
  • The use of pheromone-based lures facilitated spatial manipulation of all stages of Diorhabda carinulata, enhancing aggregation and increasing saltcedar defoliation both on established releases in Wyoming and new releases in eastern Montana.
  • This semiochemical treatment intensified D. carinulata feeding on saltcedar, causing an increase in foliar dieback and decrease in live canopy.
  • The use of Diorhabda aggregation pheromone based lures has increased the utility of biological control in the integrated management of saltcedar infesting ecologically important reaches of the Yellowstone, Missouri and Big Horn Rivers. 

Related Documents and Media

Montana State University. 27 March 2018. "Beetle odor could help tackle invasive shrub tamarisk: The pheromone-based approach targets the invasive shrub tamarisk is an alternative to herbicides and mechanical removal." ScienceDaily. 

Bichell, R. E. 11, April 2018. In battle against invasive plant, scientists seek to bring in the ground troops: Beetles. Yellowstone Public Radio

Featured Publications

Gaffke, Alexander M. ; Sing, Sharlene E. ; Dudley, Tom L. ; Bean, Daniel W. ; Russak, Justin A. ; Mafra-Neto, Agenor ; Grieco, Paul A. ; Peterson, Robert K. D. ; Weaver, David K. , 2018


Principal Investigators: 
Principal Investigators - External: 
David K. Weaver - Montana State University
External Partners: 
Alexander M. Gaffke - USDA ARS (Co-Investigator)
Megan L. Hofland - Montana State University (Co-Investigator)