Environment

Ragwort flea beetle. Biocontrol agent:
Ragwort flea beetle

Scientific name:
Longitarsus jacobaeae

Target Weed:
Ragwort
Senecio jacobaea

What do ragwort flea beetles look like?

Adult beetles are between 2.5mm and 3.8mm long and golden brown with large hind legs used for jumping.

What about their life-cycle?

Adult females lay tiny eggs, singly and in autumn, around the crown of the plants or in the surrounding soil. The larvae or grubs are white and feed on the roots, the inside of the crown and the inner leaf petioles. They develop over the winter where they do the most damage to the ragwort plant. In spring they pupate in earthen cells in the soil, with new adults emerging in early summer. 

Where are they established?

They are widespread throughout Northland.

When and how can they be harvested for distribution?

From March to May look for golden beetles and small square-shaped holes in ragwort leaves caused by beetle feeding. Their wings degenerate at this time of year, stopping them flying. Collect the beetles by using a vacuum suction machine or a butterfly net and a clean collection jar. Release a minimum of 300 beetles onto uninfected ragwort rosettes where:

• there is a density of ragwort plants of at least one plant per square metre, spread over a half hectare;
• the spread of ragwort is continuous rather than in patches;
• there will be no herbicide spraying for at least five years;
• there is limited impact on the plants from stock; and
• the site is preferably warm and sunny.

It can take up to five years for a colony to establish fully.

Find out more about controlling ragwort.