Impact of the sap-feeding Opsius stactogalus is not influenced by elevated salt concentrations in five different Tamarix taxa.
Salt cedar, Tamarix, is a genus of many Eurasian shrubby tree species in the family Tamaricaceae that is represented by one native (Tamarix usneoides E. Mey.) and two exotic (Tamarix ramosissima Ledeb. and T. chinensis Lour.) species in South Africa. The exotic Tamarix spp. have become invasive in South Africa and are targeted for biological control. Tamarix spp. are tolerant to extreme soil salinity, but it is unknown how elevated salt levels in the plant will affect coevolved insect herbivores. This study investigated whether elevated salt concentrations influenced the impact of the leafhopper Opsius stactogalus on five different Tamarix taxa. The results showed that T. chinensis excreted significantly more salt than the other Tamarix taxa. The high level of salt in the plants' tissues, however, did not show any significant effect on the feeding performance of O. stactogalus and subsequently on plant growth. There are about 25 insects that have evolved to strictly feed and survive on the halophytic Tamarix species, and among these are O. stactogalus and the Tamarix beetle (Diorhabda spp). The fact that the feeding performance of O. stactogalus across the five Tamarix taxa in this study was not significantly affected by salt addition may suggest that the Tamarix beetle (Diorhabda spp.), which is currently under quarantine investigation in South Africa, will not be influenced by the various salt concertation levels of the two exotic Tamarix species or their putative hybrids either.