ACCEPTABILITY AND SUITABILITY OF ATHEL, TAMARIX APHYLLA, TO THE LEAF BEETLE DIORHABDA ELONGATA (COLEOPTERA: CHRYSOMELIDAE), A BIOLOGICAL CONTROL AGENT OF SALTCEDAR (TAMARIX SPP.)

Authors: Milbrath, Lindsey; Deloach Jr, Culver

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2006
Publication Date: 10/1/2006
Citation: Milbrath, L.R., Deloach Jr, C.J. 2006. Acceptability and suitability of athel, tamarix aphylla, to the leaf beetle diorhabda elongata (coleoptera: chrysomelidae), a biological control agent of saltcedar (tamarix spp.). Environmental Entomology. 35:1379-1389.

Interpretive Summary: A leaf-feeding beetle has been released to control saltcedars, exotic shrubs or trees that have invaded and are damaging river systems throughout the Western U.S. Athel is an exotic evergreen species closely related to saltcedars that is not currently invasive. It is instead a moderately valued ornamental in the southwestern U.S. and northern Mexico. Three populations of the beetle, that are promising for release or have been released, were tested for the risk they may pose to athel. Adult beetles laid as many eggs on athel as on saltcedar when provided either plant by itself. However, when beetles were given a choice between saltcedar and athel, they often, but not always, laid more eggs on the saltcedar plants. Beetles fed athel survived and grew as well as beetles fed saltcedar, although their reproduction was negatively affected to some extent. The potential for damage to athel may be higher than previously thought and further tests are needed before beetles are released in areas where athel is grown.

Technical Abstract: The leaf beetle Diorhabda elongata (Brullé) sensu lato has been released in the western United States for the classical biological control of exotic saltcedars (Tamarix species and hybrids). However, athel (T. aphylla (L.) Karsten), a moderately valued evergreen species in the southwestern U.S. and northern Mexico, has not been targeted for control. All populations of D. elongata previously examined, including those promising for release in southern areas of the saltcedar infestation, develop and oviposit on athel. Therefore, we assessed more fully the acceptability and suitability of athel to three D. elongata populations (Tunisia, Crete, and Uzbekistan). All populations of D. elongata laid similar numbers of eggs on athel and saltcedar in no-choice tests. In multiple- and paired-choice tests, oviposition on saltcedar was generally greater than on athel but with some notable exceptions and inconsistencies within populations. Increasing cage size delayed the colonization of and oviposition on test plants by small groups of adult beetles, but did not change the pattern of egg-laying in the no-choice test. Survival and development were similar for Crete larvae fed athel or saltcedar. Adult size was negatively affected by a larval diet of athel. An adult diet of athel did not reduce lifetime fecundity, although it did decrease egg mass size and delayed the start of oviposition. As a result, the innate capacity for increase decreased. The potential for damage to athel by D. elongata may be higher than previously thought; this may be offset by the potential for increased invasiveness of athel.