Horizons Regional Council granted approval for insect quartet to stop wetland invader

Horizons Regional Council has been granted consent to release four biological control agents to control the spread of purple loosestrife, an invasive weed of wetlands, lakes and streams. 

The Environmental Protection Authority (EPA) has approved the import and release of four insects to target different parts of the purple loosestrife plant, Lythrum salicaria. The insects are two beetles which eat the leaves of the plant, and two types of weevil which will eat either the roots or the flowers.  
 
Horizons biodiversity and biosecurity manager Craig Davey says he is pleased approval has been granted, as using chemicals or manual removal is not an option in our lakes and wetlands.
 
“These insects are an environmentally friendlier method of controlling these plants, rather than using herbicides over water and native vegetation”.
 
“The introduction of these insects will stop the negative transformation of our precious wetland ecosystems. We have to do all we can to protect the tiny amount of these unique habitats which are home to many amazing native plant and animal species”. 
 
“Before the release of the insects, the next step is to continue our conversations with mana whenua and the wider community about this approach to habitat protection.”
 
“These insects have been successfully used for more than 30 years in the USA and Canada, where they reduced purple loosestrife infestations by up to 90 per cent. This 30 year trial showed these insects are highly unlikely to harm native or any other plants except purple loosestrife or any other animals. There is also no risk to people.”
 
“Independent experts approved these insects for import and release following a rigorous, evidenced-based investigative process which included the consideration of public submissions and international best practice and engagement with mana whenua.” says Mr Davey. 
 
“Purple loosestrife is well established in some regions, such as Canterbury, the West Coast, Wellington, and Manawatū-Whanganui, with the largest populations at Lake Horowhenua. However, it has yet to spread more widely throughout the country and the release of these insects will help to stop, or dramatically slow, expansion.”
 
Mr Davey says purple loosestrife was introduced to New Zealand as an ornamental herb before naturalising in the wild in the 1950s. An established plant can create over 2.5 million seeds.