The biological control program against gorse in New Zealand

Gorse (Ulex europaeus L.: Fabaceae) has been a serious weed in New Zealand for over 100 yr, and continues to invade pastoral land, forest plantations, and vulnerable nat-ural habitats. It has beneficial uses, but these are far outweighed by the costs. Gorse was once an important hedge plant, and until 1982, seed-feeding insects were the only biolog-ical controls considered appropriate. Exapion ulicis Forst. was released in 1931, and destroys about 35 % of the annual seed crop. Six control agents have been introduced since 1988. Cydia succedana (Dennis and Schiffermüller) was released in 1992. Assessment at 1 site shows that the 2 seed-feeding insects can destroy about 90 % of the annual seed crop. Gorse spider mite (Tetranychus lintearius Dufour) was introduced from several sources in Europe in 1989 and 1990, and established widely. Mite outbreaks severely damage plants, and reduce flowering, but populations large enough to kill mature gorse plants over wide areas cannot be sustained, probably because of predation. The gorse thrips, Sericothrips staphylinus Haliday, was introduced in 1990. It has spread only slowly, but significantly damaged gorse foliage in experimental studies. The foliage-feeding moths Agonopterix ulicetella (Stainton) and Pempelia genistella (Duponchel) have been released. Establishment is not yet certain. The scythridid moth, Scythris grandipennis (Haworth), has also been released, but it did not establish. No further releases are planned. Development of a bioherbicide augments the classical approach to biological control of gorse. The paper discusses the impact of control agents, and the future of the research. The New Zealand program has provided information and control agents to similar program