Impacts of tamarisk biocontrol (Diorhabda elongata) on the trophic dynamics of terrestrial insects in monotypic tamarisk stands

Combating tamarisk (Tamarix spp.), an exotic tree species that has invaded 1-1.6 million hectares of riparian land in the Midwestern United States, with the introduced leaf beetle Diorhabda elongata provides an opportunity to evaluate how the trophic spectra of terrestrial insects respond to a herbivorous biocontrol. To evaluate this restoration approach and the interaction biocontrol may have with terrestrial insect populations, I quantified trophic unit richness and abundance and common family abundance of resident insect populations while also measuring biocontrol abundance and status during the previous season (present or not present). These measurements were taken four times throughout one season in monotypic tamarisk at two locations in Grand County, Utah. Biocontrol abundance was lower when biocontrol had been present in the previous season. Predator, omnivore and herbivore richness and omnivore, Histeridae, Lygeaidae and Formicidae abundance showed a relationship with biocontrol abundance. When biocontrol had been present in the previous season, predator richness and, Histeridae abundance was higher while when biocontrol had not been present in the previous season herbivore richness and detritivore, Lygeaidae and Elateridae abundance was higher. The results suggest relationships exist between D.elongata and multiple members of the trophic spectra of terrestrial insects that changes when biocontrol have been present for more than one season. If D. elongata are adding connections and complexity to the trophic spectra through these relationships with terrestrial insects than the use of biocontrol in monotypic tamarisk stands may help preserve what is left of the trophic web in the invaded ecosystem. Understanding the side effects of a biocontrol on the trophic structure of an ecosystem is essential to land management. At the same time, this work provides a more thorough understanding of the effect of herbivorous biocontrol on the trophic ecology of disturbed ecosystems.