Saltcedar (Tamarix sp.) is an invasive riparian shrub/tree spreading through the western US. Diorhabda elongata (Coleoptera: Chrysomelidae) is a biological control for saltcedar. Ecotypes from China and Greece have been released in the western US. Ecotypes from Fukang, China have established in northern locations and ecotypes from Posidi and Crete, Greece are establishing in southern locations. It is likely that distribution of these ecotypes will overlap in the future. The objective of this experiment was to monitor the differences between Chinese and Greek ecotypes in field cages and to determine the effects of mixing populations.

Chinese and Greek ecotypes will mate and produce viable eggs when confined; however, all of the F1 offspring are sterile. The consequences of hybrid matings could disrupt long-term population dynamics in a mixed field population, slowing population growth or causing localized extinction of one ecotype. While it is still unknown if the Chinese and Greek ecotypes can coexist, in a no-choice controlled environment the two ecotypes will readily mate with each other.

Population and mating studies were carried out in a two year experiment. Large field cages were setup with three different beetle treatments: Greek, Chinese, and mixed Greek and Chinese. Saltcedar defoliation, and the density of adults, eggs and larvae were estimated in all cages. The first year, Greek populations peaked at 500 adults resulting in 100% defoliation while Chinese populations reached 120 adults resulting in 60% defoliation. The mixed Greek and Chinese cages had no population growth and no defoliation.