Most species of Tamarix originate in Eurasia and at least five species have become invasive around the world, including South Africa. However, T. usneoides is indigenous to southern Africa, where the potential for biological control of the invasive species is being investigated. Recent research on the invasive species is reviewed here with particular reference to these South African biocontrol efforts. The successful biological control programme against invasive Tamarix in the USA, using several species of ''Tamarisk beetle'', is being used as a guide for the South African research. The South African programme is complicated by firstly, the presence of the indigenous T. usneoides which raises the precision of host-specificity required, and secondly, the introduced and indigenous Tamarix have a high intrinsic value for phytoremediation of mine tailings dams in South Africa. The phylogenetic proximity of these Tamarix species to each other has contributed to this challenge, which has nevertheless been successfully addressed by molecular techniques used to separate the species. In addition, classical morphological techniques have been used to separate the Tamarisk beetles, so that now they can generally be matched to Tamarix tree species. Overall, it is concluded that given the broad knowledge now available on the ecology and identity of both the trees and their biocontrol agents, the prospects for successful biological control of Tamarix in South Africa are good.

Several countries globally, including South Africa, have been invaded by at least one of five species of Tamarix. South Africa therefore considered using one or more species of leaf-feeding beetles in the genus Diorhabda (Coleoptera: Chrysomelidae), including Diorhabda carinulata, against invasive T. ramosissima and T. chinensis, since the beetles are highly damaging in the USA. The situation in South Africa is possibly more complicated than that in the USA because there is an indigenous species, Tamarix usneoides, which could potentially serve as a host for the beetles. To investigate this possibility, a series of field and laboratory host specificity tests were conducted using D. carinulata against invasive target Tamarix species and the indigenous non-target T. usneoides. Field tests showed that D. carinulata had a preference for invasive Tamarix species, but readily settled and laid eggs on T. usneoides. Laboratory paired-choice tests showed that adult beetles preferred T. usneoides over T. chinensis and preferred T. ramosissima over T. usneoides, for both feeding and oviposition. Laboratory no-choice tests showed the egg-to-adult survival rate to be higher for individuals reared on T. usneoides than on T. ramosissima. Furthermore, the fecundity of females reared on T. usneoides was higher than that of females reared on T. ramosissima. Diorhabda carinulata is thus not a suitable biocontrol agent against invasive Tamarix in South Africa. An alternative biocontrol agent is currently being sought, and a short-list of candidate agents has already been compiled.