Biological control of gorse in New Zealand

[1] Gorse was introduced to New Zealand by missionaries during the early stages of European colonization[2] and quickly became a popular hedge plant, remaining in widespread use as fence material until the 1950s, when it was largely superseded by wire and posts.

[3] It established itself very quickly, and the lack of natural predators or other controls meant that it spread rapidly,[2] flowering for longer periods and growing to a larger size than it did in Europe.

[4] Gorse is an extremely hardy plant which forms dense thickets over what was once native forest or productive farmland; any attempts to destroy it by burning or spraying often result in rapid, widespread regrowth.

[7] However, experts like ecologist Ian Popay argue that the forest that results is different to that which would have grown without the presence of gorse, and that this alteration is not "natural".

[4] Hawke's Bay Regional Council holds the view that cultivating native forest in this fashion is risky and cannot be recommended,[4] although the Department of Conservation provides a practical guide to doing so.

[11] Research in the United Kingdom in 1928 suggested that Apion ulicis, as it was then known, would be an effective control agent; on the strength of these recommendations, it was imported into New Zealand that year.

[1] Despite this, its apparent success — regular destruction of around 90% of the seeds produced in the spring — contributed to the delay in investigating further biological control agents until much later in the century.

[1] Native to Europe, Tetranychus lintearius is a host-specific mite that lives in colonies under sheets of silk on gorse plants.

[10] Introduced in 1990, the host-specific gorse thrips is widely established,[6] but has not spread far beyond its release sites[1] because winged individuals are relatively rare.