Comparing host-plant acceptance of Tamarix parviflora (Caryophyllales: Tamaricaceae) by field-established and laboratory populations of Diorhabda elongata (Coleoptera: Chrysomelidae), a biological control agent of saltcedars

A change in host plant acceptance of invasive Tamarix parviflora (Caryophyllales: Tamaricaceae) by Diorhabda elongata (Coleoptera: Chrysomelidae) beetles was evaluated by comparing preferences of the northern California field-established population to its source colony. In a caged experiment, beetles were given a choice between T. parviflora and an alternative high quality host, Tamarix ramosissima. Oviposition was recorded as total egg clusters and total eggs on each substrate (T. parviflora, T. ramosissima and the cage). During two preliminary experiments in 2007, the field population did not show significant differences in egg laying on either host plant for number of egg clusters or total eggs. In 2008, the laboratory source population showed highly significant preference for T. ramosissima, consistent with previously published data (For Egg Clusters F=41.45, df=1,8, p=.0002; For Total Eggs F=28.8, df=1,8, p=.0007). In the same year the field population also showed statistically significant preference for T. ramosissima over T. parviflora, but the magnitude of preference was much lower, with egg clusters and eggs more evenly distributed on both hosts (For Egg Clusters F=13.99, p=.0057; For Total Eggs F=17.49, df=1,8, p=.003). An increase in host plant acceptance of T. parviflora by the field population may have contributed to delayed establishment of this biological control agent at Northern California release sites where T. parviflora is the only available host, and will be investigated in further studies.