Target pest: Rosa rubiginosa (Rosales: Rosaceae), sweet briar
Agent introduced: Megastigmus aculeatus (Hymenoptera: Torymidae), rose seed chalcid
Syrett (1990), Harman (1996) - accidental introduction.
Syrett (1990), Harman (1996) - first recorded in New Zealand in the 1960s.
Syrett (1990) - Rosa rubiginosa hips were collected from nine sites in Otago and Canterbury during winter 1987. Megastigmus aculeatus was present at all sites, with percentage of hips infested ranging from 26 to 70%.
Impacts on target:
Syrett (1990) - in the 1987 Canterbury and Otago study, a mean of 7.7% of seeds were infested (range 1.5 - 12.4%). A previous study at a number of South Island sites in the 1960s recorded a mean of 12.0% (range 0 - 29.5%) of seeds infested. While these figures are high compared to infestation rates recorded in Europe, they are too low for M. aculeatus to be a major factor in limiting establishment of new plants, but there is insufficient evidence to conclude that seed feeding by this wasp does not influence populations of sweet briar in some areas.
Harman HM, Syrett P, Hill RL, Jessep CT. (1996). Arthropod introductions for biological control of weeds in New Zealand, 1929 - 1995. New Zealand Entomologist, 19(1): 71-80
Syrett P (1990). The rose seed chalcid Megastigmus aculeatus Swederus (Hymenoptera: Torymidae) on sweet briar, Rosa rubiginosa, in the South Island tussock country. New Zealand Entomologist 13: 34-38 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.566.3684&rep=rep1&type=pdf