Fungus gnats and other Diptera in South African forestry nurseries and their possible association with the pitch canker fungus

Fusarium circinatum is the causal agent of a serious disease of seedlings in South African pine nurseries. Insects, especially fungus gnats (Diptera: Sciaridae, Mycetophlidae), are suspected of transmitting this fungus in nurseries. The aim of this study was to ascertain which species of gnats are present in South African pine nurseries, and to consider whether these and other Diptera carry F. circinatum. Dipteran fauna were surveyed in four major forestry nurseries between 2000 and 2001. Fungi were isolated from these flies and the resulting Fusarium species were identified. Bradysia difformis was the only fungus gnat species found and it occurred in all nurseries. Other Dipteran families collected included Agromyzidae, Cecidomyiidae, Chironomidae, Ephydridae, Muscidae, Simulidae and Tachinidae. This is the first report of B. difformis in South Africa. Fusarium circinatum was not isolated from any of the Diptera collected. Fusarium oxysporum and F. stilboides were isolated from Chironomidae, but these fungi are not considered important pathogens in the nurseries surveyed.