Field demonstration of a semiochemical treatment that enhances Diorhabda carinulata biological control of Tamarix spp.

Abstract

The northern tamarisk beetle Diorhabda carinulata (Desbrochers) was approved for release in the United States for classical biological control of a complex of invasive saltcedar species and their hybrids (Tamarix spp.). An aggregation pheromone used by D. carinulata to locate conspecifics is fundamental to colonization and reproductive success. A specialized matrix formulated for controlled release of this aggregation pheromone was developed as a lure to manipulate adult densities in the field. One application of the lure at onset of adult emergence for each generation provided long term attraction and retention of D. carinulata adults on treated Tamarix spp. plants. Treated plants exhibited greater levels of defoliation, dieback and canopy reduction. Application of a single, well-timed aggregation pheromone treatment per generation increased the efficacy of this classical weed biological control agent.

Using Chemical Ecology to Enhance Weed Biological Control

“…New research has demonstrated that for D. carinulata, field deployment of lures containing the aggregation pheromone (but with no sticky traps as above) resulted in increased densities of the agent in targeted Tamarix stands [23,54]. The deployment of the aggregation pheromone effectively allowed researchers to dictate where the beetles aggregated and fed.…”

“…For Tamarix, two years of defoliation commonly results in a 25-33% reduction in plant canopy. However, when D. carinulata was directed to target plants with the aggregation pheromone, there was a 73-79% reduction in canopy size after two years of defoliation [23,54].…”

“…The D. carinulata pheromone blend (blue triangles) is placed on trees targeted for removal. Beetles are attracted (black arrows) to the pheromone, resulting in elevated D. carinulata populations and accelerated defoliation of the shrubs [23,54]. Targeted areas with blue triangles will be defoliated early in the season while the flycatcher nesting territory will remain green until later, after birds have fledged.…”

“…Putative aggregation pheromones for these species have been identified and chemical synthesis has been developed [21,59]. Behavioral activity in the field remains to be shown but should the compounds prove to be aggregation pheromones they could be deployed during new releases to help retain larger numbers of the agent at the release site since they may not be capable of emitting their own pheromone shortly after being released [54]. Monitoring is likely to be enhanced by using pheromones to track populations, and density manipulations could be conducted to achieve greater impacts from the established populations.…”

“…Once semiochemicals have been identified in weed biocontrol agents, the last barrier to incorporation into weed management programs is the availability of these compounds to biocontrol practitioners and resource managers. For example, the Diorhabda aggregation pheromones are not commercially available and so researchers must either synthesize the pheromone or work with chemists to synthesize it prior to initiating experiments [15,23,50,54]. In addition to pheromone availability, field release methods need to be developed prior to deployment.…”