Comparison of Laboratory and Ecological Host Range of the Saltcedar Leaf Beetle with Respect to Native Non-Target Frankenia species

Authors: Herr, John; Carruthers, Raymond; Deloach Jr, Culver

Submitted to: Proceedings of the California Conference on Biological Control
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: 3/30/2007
Citation: Herr, J.C., Carruthers, R.I., Deloach Jr, C.J. 2007. Comparison of Laboratory and Ecological Host Range of the Saltcedar Leaf Beetle to Native Non-Target Frankenia species. in: Hoodle, M., Johnson, M. Editors. Proceedings Fifth California Conference on Biological Control, University of California, Riverside, California, p. 148-151.

Interpretive Summary: Laboratory and field experiments were conducted to determine which native and introduced plants would be fed on by a beetle (Diorhabda elongata), introduced to control invasive saltcedar (trees in the genus Tamarix). Beetle larvae were able to feed and develop to the adult stage on native non-target plants in the genus Frankenia, and in some cases their survival rate was not significantly different than when fed on saltcedar (Tamarix ramosissima). However, adult beetles showed a clear preference for saltcedar, and laid significantly more eggs on it than on the native plants, when tested in laboratory cages. Tests run in large outdoor field cages produced lower egg-laying on the native Frankenia (4.3 percent of eggs laid on the native plant, compared with 11.4 percent in the lab tests). In an “open field test” (no cages, test plants exposed to natural conditions in the field) the beetles laid no eggs on the native plants, but did lay eggs on adjacent saltcedar test plants. These experiments indicate that although D. elongata will feed and lay eggs on native Frankenia the laboratory, they may be less likely to do so under natural field conditions.

Technical Abstract: Laboratory and field host specificity tests were conducted with the saltcedar biocontrol agent, Diorhabda elongata (Coleoptera: Chrysomelidae) from Crete, to assess the potential risk of impact to non-target North American Frankenia species. Larval survival was not significantly different between Tamarix ramosissima (saltcedar) and the native, non-target plant Frankenia salina, but was significantly lower on F. jamesii. In laboratory cage studies, adult D. elongata laid significantly more eggs on T. ramosissima in a choice test but showed very little discrimination between Tamarix and Frankenia species in a no choice test. The percentage of eggs laid on F. salina decreased from 11.4 in laboratory cages to 4.3 in field cages to zero in an open field test, suggesting that the true ecological host range of D. elongata may be more limited that laboratory tests predict.