Scottish ‘Laddies’ Flown in for Genetic Rescue
A novel experiment is underway to improve the vigour of heather beetles (Lochmaea suturalis).
The beetles have been established in Tongariro National Park to control heather (Calluna vulgaris) planted by a park superintendent in the 1800s wanting to provide habitat for grouse. Although the grouse never established, heather soon became a serious weed, displacing native vegetation and spreading over vast areas of the Central Plateau. Once it became apparent that biocontrol offered good prospects, heather beetles were collected from several sites in the UK and released here in 1996 following extensive efforts to eliminate a microsporidian disease. This involved considerable line-rearing of individual beetles and culling of any diseased lines until a clean population was achieved.
At high densities heather beetles do a fantastic job of killing heather, reducing the need to apply herbicides, which are expensive and have undesirable effects on native vegetation. However, while there have been some impressive outbreaks in recent years, overall the beetle populations have been painfully slow at establishing and spreading. Research has been underway to try to identify what factors might be limiting them. Several theories have been put forward over the past decade including:
- Predators, parasitoids or diseases were attacking the beetles in New Zealand.
- Climate match between UK and the Central Plateau was not close enough.
- Insufficient nitrogen in the foliage here to support the beetles.
- The beetles were genetically constrained, small and not able to adapt to New Zealand conditions.
Careful research has shown that pressure from natural enemies is not an issue, but the nitrogen content of the heather foliage is extremely low compared with heather growing in the UK. The genetic diversity among the New Zealand heather beetles is also low, as a result of genetic bottlenecking during the disease eradication phase, and beetles here are considerably smaller than their UK counterparts. Experiments conducted to simulate winter conditions showed that the fat reserves held by the beetles were an important factor in determining their ability to survive over winter. Their small size, in combination with the low nutritional value of the heather, means that the beetles find it difficult to build up sufficient fat reserves to survive winter on the Central Plateau.
With this in mind Paul Peterson (Landcare Research) and Paul Barrett (Massey University) went to Scotland in May to collect some ”nuggety” male heather beetles to mate with the smaller females back here in New Zealand. “Climate and body size data suggest that beetles of Scottish origin will be better adapted to the harsh climatic conditions found on the Central Plateau and past experience suggests that Scottish populations are less likely to be infected with the microsproridian disease than populations from England,” said Paul. “By bringing in Scottish males for only brief matings with New Zealand females we further reduce the risk of infection because the disease is not sexually transmitted,” he added.
On their journey from Scotland, the beetles not only faced long flights with no in-flight entertainment or meals, but also had to endure inspections at customs and were subjected to a scrupulous hygiene regime on arrival into containment where they were checked for diseases. It was little wonder that they were initially a bit reticent about “performing” when they were first introduced to the females! “Despite our observations of many matings, only a few females have produced fertile eggs. We have re-mated the same pairs in the hope this will stimulate more females into egg production,” said Lindsay Smith, who is caring for the beetles in containment at Lincoln. Any offspring will be checked to make sure they are disease- free before releasing them into Tongariro National Park.
This project represents a novel approach to explore the possibility of enhancing the performance of already established biocontrol agents so that they can better adapt to the local conditions and more effectively control the target weed. Only time will tell if this genetic rescue mission is successful.
This project is funded by the Ministry of Business, Innovation and Employment as part of Landcare Research’s Beating Weeds Programme. Paul Peterson’s trip to Scotland was funded by a Queen Elizabeth II Technicians’ Study Award.