A Re-Assessment of Mortality Factors Associated with the Bud-Galling Midge, Dasineura strobila, a Biological Control Agent of Leptospermum laevigatum in South Africa

Abstract

The bud-galling midge, Dasineura strobila Dorchin (Diptera: Cecidomyiidae), is one of two biological control agents that have been introduced into South Africa to control the invasive tree, Australian myrtle, Leptospemum laevigatum (Gaertn.) F.Muell. (Myrtaceae). Whilst both agents are established and widespread, L. laevigatum continues to grow vigorously and spread within its range. Earlier studies reported decreasing populations and reasonably high levels of mortality of the midge; however, the role of this mortality in regulating D. strobila populations was not proven. A re-assessment of the mortality factors on D. strobila confirmed the continued presence of both parasitoids and a predatory mite, accounting for only 5 % and 4.9 % mortality respectively over a two-year period. Whilst outbreaks of predatory mites could occur, mortality is not believed to be a driving force in regulating D. strobila populations. Although further studies are required to clarify the situation, it is suggested that despite the presence, and relative abundance of the midge, its impact as a biocontrol agent for Australian myrtle, remains negligible.