Biological control of lesser calamint
Lesser calamint is an aromatic perennial herb that has been introduced to New Zealand from Europe. Currently present on the east coast of the North Island, lesser calamint is considered an emerging weed; it is affecting desirable pasture species and having negative economic impacts. CABI is conducting field surveys and searching for natural enemies from lesser calamint’s area of origin in Europe that could be introduced in New Zealand as biological control agents.
So, what’s the problem
Lesser calamint (Calamintha nepeta) is an aromatic perennial herb in the mint family, Lamiaceae. Originating from Europe, it has been introduced to New Zealand where it is a weed on the east coast of the North Island. It is not palatable to livestock and it is displacing desirable pasture species. Although not yet widespread, lesser calamint is already having negative economic impacts on infested properties.
Controlling lesser calamint is difficult. Due to its rhizomatous root system and small hairy leaf area, using chemicals is not feasible, and mechanical control is impractical. However, biological control, i.e. introducing natural enemies from the weed’s area of origin, could be a valid option.
One reason for the plant’s impact may be the absence of natural enemies that attack it in its area of origin. The challenge is to find natural enemies that attack lesser calamint but do not damage related popular herb or native species.
What is this project doing?
A preliminary literature survey revealed several herbivores and fungal pathogens that may have potential as biological control agents for lesser calamint.
In 2018, CABI was asked by Landcare Research, New Zealand to conduct surveys for potential agents in the native range of lesser calamint in Europe, and to collect plant material for DNA analysis to help determine this species’ area of origin in New Zealand.
Field surveys were conducted in southern Switzerland, southern France and Italy. Plants were checked for exo- and endophagous herbivores, whilst fungal pathogens and leaf samples were collected for molecular analyses. So far, a shoot-boring moth, a gall midge, a leaf mining beetle and several externally feeding lepidopteran larvae were found. Immature stages of herbivorous insects were reared to adults and will be sent to taxonomists for identification. In addition, further surveys will be conducted in other parts of southern Europe.
Waikato Regional Council, New Zealand
Horizon's Regional Council (Manawatu-Wanganui region), New Zealand
Hawke's Bay Regional Council, New Zealand
Hawke's Bay Lesser Calamint Control Group, New Zealand