Background/Question/Methods Riparian communities heavily occupied by the exotic plant, tamarisk (tamarix spp.), can have dramatically different composition and biodiversity of flora and fauna as compared to historical native plant communities.  Biocontrol for tamarisk, tamarisk leaf beetle (Diorhabda elongata), was released to control tamarisk in the United States in 1999 and is flourishing in several riparian areas in at least six states.  How the biocontrol beetle, D. elongata, affects these already disturbed ecosystems is largely unknown.  In an effort to elucidate the relationship between D. elongata and the trophic ecology of monotypic tamarisk stands, we evaluated the trophic dynamics of terrestrial arthropods with different biocontrol abundance.  To do this, we measured the abundance and richness of terrestrial insects at four locations with varying levels of biocontrol abundance in Grand County, Utah.  We sampled 80 paired pitfall traps between all locations during the period when the D. elongata were active: 26-June-08, 9-July-08, 2-Aug-08, and 16-Aug-08.  Repeated Measures Analysis of Variance was used to determine how each of the trophic units and families reacted to different biocontrol abundance throughout the season.  We hypothesized that as the biocontrol abundance increased, predator and omnivore abundance would increase while herbivore and detritivore abundance would decrease.  

Results/Conclusions

A relationship existed between biocontrol presence and trophic units’ abundance; however, differences in biocontrol abundance only affected one trophic units’ abundance and had no effect on any trophic units’ richness.  At the family level, Cryptophagidae and Histeridae abundance responded positively to biocontrol at each collection date, while Formicidae and Rhaphidophoridae responded negatively to the initial abundance of biocontrol.  Carabidae did not react to biocontrol abundance but was more abundant when tamarisk had not been defoliated by biocontrol.  The results suggest that although predator, omnivore, and detritivore abundance responded to biocontrol presence at each collection, only omnivores reacted to different abundances of biocontrol.   Thus, the trophic response of terrestrial insects to the introduction of biocontrol may not be as dramatic as we initially hypothesized.  Although preliminary, these data are the first to evaluate the impact that D.elongata have on terrestrial insects in monotypic tamarisk and serve as a foundation for future work to more thoroughly understand trophic interactions between introduced species and trophic dynamics.