A successful biocontrol agent in the USA, Diorhabda carinulata (Coleoptera: Chrysomelidae) on Tamarix spp. (Tamaricaceae), rejected in South Africa due to insufficient host specificity

Abstract

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.