Predicting the likely success of biological control of hawkweeds in New Zealand
Pauline SyrettA, Lindsay SmithA, Gitta GrosskopfB and Colin MeurkA
A Landcare Research, PO Box 69, Lincoln, Canterbury, New Zealand.
B CABI Bioscience, 1 chemin des Grillons, Delémont, Switzerland.
Five species of hawkweed (Hieracium pilosella, H. praealtum, H. caespitosum, H. aurantiacum and H. lepidulum), originating from Europe, are invasive in native grassland ecosystems in New Zealand, displacing desirable environmental and agricultural species. A rust fungus and five insect species have been identified for introduction as complementary biological control agents. The rust fungus Puccinia hieracii var. piloselloidarum is now widely established as the result of an accidental introduction, but attacks only some forms of H. pilosella. Two insect species, a plume moth, Oxyptilus pilosellae, and a gall wasp, Aulacidea subterminalis, have already been released in the field, and two syrphid flies (Cheilosia urbana and C. psilophthalma), and a gall midge (Macro-labis pilosellae) are expected to be released shortly. The six control agents should complement each other because they attack different parts of the plant, and between them are predicted to affect all five weedy hawkweeds. All six agents are likely to achieve significant levels of damage on H. pilosella, three of them will target H. praealtum, four of them should suppress H. caespitosum and H. aurantiacum. Only one insect species, the root-feeding C. urbana, is predicted to be as damaging to H. lepidulum as to H. pilosella, so further control agents are likely to be needed to suppress this non-stoloniferous hawkweed.
Plant Protection Quarterly (2001) 16 (4) 172-176.