The Clover Root Weevil Invasion: Impact and Response of the New Zealand Pastoral Industry 1996-2012

Clover root weevil, Sitona lepidus Gyllenhall (Curculionidae: Coleoptera), was first reported in New Zealand in 1996. With few natural enemies or competitors, it rapidly became a major pest of white clover. Its strong flight capability, tendency to be transported in agricultural machinery and vehicles, and wide climatic tolerance enabled it to spread the length of the country (1,600 km) by 2010. The most damaging stage is the larva, which attacks the roots, root nodules and stolons of clovers, reducing herbage production (particularly in spring), pasture clover content, and nitrogen fixation. From the time of the initial invasion, the pastoral industry supported research into management as insecticides were not a viable option. Nitrogen fertiliser applications after grazing were recommended to maintain production. Field evaluations showed that white clovers with good general agronomic adaptation survived better under weevil pressure than less-adapted clovers. In 2006, a parasitic wasp, Microctonus aethiopoides Loan (Braconidae: Hymenoptera), was introduced from Ireland for biological control of S. lepidus. It has also established and dispersed very rapidly, and often suppresses weevil populations within 2 – 3 years of its establishment in a new locality. Involvement of industry field consultants was an essential aspect of the biological control release programme in the North Island where the weevil was already widespread before M. aethiopoides was introduced