Field-based surveys and laboratory tests indicate that candidate biocontrol agents for African lovegrass from South Africa are not suitable for release in Australia

Abstract

African lovegrass, Eragrostis curvula (Schrad.) Nees (Poaceae), is a perennial grass native to southern Africa that has become problematic in many countries, most notably in Australia. A biological control programme against E. curvula in Australia has been initiated to mitigate the plant's negative impacts. We present field-based host-specificity observations of natural enemies in the native distribution in South Africa and validate these observations with laboratory based no-choice host-specificity tests. Only three insect species were consistently found utilising E. curvula, namely two stem-galling wasps belonging to the genus Tetramesa (Hymenoptera: Eurytomidae), and a shoot-galling fly (Diptera: Chloropidae). The shoot-galling fly was found to utilise grasses from multiple non-target grass genera and was thus rejected. Both Tetramesa species were recorded on multiple native African Eragrostis species during field host-range surveys, and this relatively broad host range was confirmed by both wasp species completing development on several native Eragrostis species under no-choice conditions in the laboratory. At least three native Australian species (E. parviflora, E. trachycarpa, E. leptocarpa) are predicted to be suitable hosts for both Tetramesa species. Neither Tetramesa species are therefore likely to be suitably host specific for release on E. curvula in Australia. The recent discovery of an adventive population of one of the South African Tetramesa on E. curvula in Australia provides an opportunity to test whether the predicted host range of the species is realised in the introduced distribution.