Acceptability and Suitability of Athel,Tamarix aphylla, to the Leaf BeetleDiorhabda elongata(Coleoptera: Chrysomelidae), a Biological Control Agent of Saltcedar (Tamarixspp.)

The leaf beetle Diorhabda elongata (Brulle) 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), an exotic, moderately valued evergreen species in the southwestern United States and northern Mexico, has not been targeted for biological 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. For Crete beetles, survival and development were similar for 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; however, this may be offset by the potential for increased invasiveness of athel.