Host preference between saltcedar (Tamarix spp.) and native non-target Frankenia spp. within the Diorhabda elongata species complex (Coleoptera: Chrysomelidae)

Since its release in 2001 for the biological control of saltcedar (Tamarix spp., Tamaricaceae), the leaf beetle Diorhabda elongata (Brullé) from China and Kazakhstan, has become successfully established in many locations in the western United States. However, it failed to establish in the southern and western portions of the saltcedar infestation, creating the need to test additional populations of the beetle from other areas within its region of origin. The host specificity of seven Eurasian populations of D. elongata was evaluated by testing larval development and adult ovipositional preference on a variety of non-target agricultural, ornamental and native plants, with emphasis placed on native Frankenia spp. (Frankeniaceae), which were shown to be laboratory hosts in previous tests. No larvae survived on any of the non-target test plants except for Frankenia spp., where survival to the adult stage ranged between 15% and 92%, and was often not significantly different from survival on Tamarix controls. Adult Diorhabda from Crete laid significantly more eggs on Tamarix ramosissima Ledebour than on Frankenia spp. in a multiple-choice oviposition test but showed very little discrimination between Tamarix and Frankenia species in a no-choice test. In paired-choice tests, all seven Diorhabda populations laid significantly more eggs on T. ramosissima than Frankenia salina (Molina) I.M. Johnston. However, the percentage of total eggs laid on F. salina ranged from 0.8% to 15.7%, suggesting that some utilization of this native plant might occur in the field, despite the presence of a preferred host plant. Significant differences were found between some Diorhabda populations in the percent of total eggs laid on F. salina, indicating a variable degree of risk to these non-target plants.