Progress on the potential biological control programme for invasive Tamarix in South Africa

Progress on the potential biological control programme for invasive Tamarix in South Africa
Danica MARLIN1, Etienne Smit1, Marcus J. Byrne1,2
1School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
2Centre for Invasion Biology, School of AP&ES, University of the Witwatersrand, Johannesburg, South Africa

Tamarix is a riparian tree with tiny white-to-pink flowers. All of the species in the genus except T. usneoides, which is indigenous to South Africa, originate in Eurasia and at least four have become invasive in South Africa. South Africa is using the successful USA biological control programme as a template to develop biocontrol agents against the same invasive Tamarix species. However, 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, all Tamarix species have a high intrinsic value for phytoremediation of mine tailings dams in South Africa. The potential biocontrol agents, Tamarisk beetles (Diorhabda spp.), were imported into quarantine in South Africa during September 2015. Preliminary results in quarantine indicate that oviposition (number of egg clusters) is higher on the invasive species (T. chinensis), but the egg clusters are larger (number of eggs/cluster) on hybrids with the indigenous species (T. ramosissima x T. usneoides) than on the invasive T. chinensis. The larvae had a faster development rate and more larvae survived to 3rd instar on the hybrid compared to the invasive species. Furthermore, additional and preliminary field host-specificity test conducted in the USA showed that the beetles do not have a preference for T. usneoides under field conditions. Thus, the prospects for successful biological control of Tamarix in South Africa are good.