Impact of the flower-galling midge, Dasineura rubiformis Kolesik, on the growth of its host plant, Acacia mearnsii De Wild, in South Africa

Acacia mearnsii (black wattle), although recognised as being extremely invasive and problematic in South Africa, is cultivated as an important commercial plant in parts of the country. Following the introduction of a flower-galling midge, Dasineura rubiformis (Cecidomyiidae), into the Western Cape Province for biological control of A. mearnsii, trials to confirm that galling would not affect growth rates of the host-plant were necessitated before the midge could be more-widely distributed. Insecticide exclusion of the midge from selected branches of the plant enabled comparison of growth rates of branches with high and low levels of galling. Over fifteen months the increment in branch diameter was greater on highly galled branches than on lightly galled branches with pods. This result indicates that D. rubiformis, while reducing seed set to very low levels, does not negatively affect growth of its host and that the midge will have no detrimental effect on the wattle forestry industry in South Africa.