All plants have a biochemical profile, which can be altered by abiotic conditions such as light and nutrient availability and biotic factors such as herbivory and plant pathogens. In issue 99 we wrote about plant metabolomics (the study of plant biochemistry at the molecular level) and how it can affect the success of biocontrol. The gist of the article was that a plant’s biochemical profile can significantly affect the performance and population dynamics of insect biocontrol agents feeding on the plant. Therefore, understanding the biochemistry of plants and their biochemical phenotypes (observable characteristics) may help us understand the success or failure of weed biocontrol programmes.
In a recent study, researchers from Massey University, AgResearch, the James Hutton Institute in Scotland, and MWLR investigated the biochemical phenotypes of heather (Calluna vulgaris) sourced from its native range in Scotland and its invasive range in New Zealand. The researchers were particularly interested in heather as a study system because its introduced biocontrol agent, the heather beetle (Lochmaea suturalis), was difficult to establish in New Zealand and initial performance was inconsistent.
To study the biochemical phenotypes, scientists analysed primary and secondary metabolites (intermediate or end products of metabolism) in heather from Scotland and from the Central Plateau in New Zealand. Foliage samples were collected in the Northern and Southern Hemisphere summers, as were soil samples. The foliage samples were analysed for their chemical compounds and soil samples for their nutrient composition.
Image: heather invasion on the Central Plateau in 2003.
The chemical analysis found that the biochemical profile of heather plants growing in New Zealand is significantly different from that of plants in Scotland. “We found higher levels of defensive secondary metabolites in New Zealand heather samples compared to those from Scotland, which may have implications for the performance of the heather beetle in New Zealand, in terms of its survival, reproduction and development rates. These factors are linked to intrinsic rates of increase for insect populations, and could therefore have a significant effect on their success as a biocontrol agent,” said Paul Peterson, a senior technician from MWLR involved in this work.
The different biochemistry could be explained by the soil and UV intensity levels at the New Zealand heather sites: compared to the sites in Scotland, New Zealand soils have lower nutrient availability and higher UV intensity levels. Both of these have been found in other studies to lead to higher levels of chemical defence compounds in plants, although this was not directly tested in this study. Experimental tests in controlled conditions would be needed to confirm the direct effects of soil nutrients and UV intensity on heather’s biochemical phenotypes.
Image: heather beetles.
So, what does this mean for the heather beetle in New Zealand? These findings suggest that the altered biochemical phenotype of heather in the invaded range in New Zealand could impair the success of the heather beetle. Since heather plants in New Zealand were found to have higher chemical defences, the plants could be more resistant to feeding by the beetles, which could have made it more difficult for them to successfully establish and build up high numbers. This may explain, at least in part, why the heather beetle was so difficult to establish and why its initial performance as a biocontrol agent in New Zealand was poor.
“Further research is needed to confirm the direct effects of soil nutrients and ultraviolet light on heather’s biochemistry and to understand their impact on biocontrol agents,” said Paul Barrett, the research leader from Massey University. “This study shows that plant biochemical analyses are a valuable tool for understanding the success or variability of biocontrol agents.”
For heather beetles in New Zealand, the team at MWLR is continuing research efforts to understand why the heather beetle is now well established, with outbreaking populations that are having substantial impacts on heather over a large area of Tongariro National Park. More on this complex insect–weed system in future issues!
Further reading:
Barrett DP, Subbaraj AK, Pakeman RJ, Peterson P, Clavijo McCormack A 2024. Metabolomics reveals altered biochemical phenotype of an invasive plant with potential to impair its biocontrol agent’s establishment and effectiveness. Scientific Reports 14: 27150.
Paul Barrett was funded by the QEII Technicians’ Study Award; Paul Peterson was funded by MWLR’s Beating Weeds Programme, which is funded by the Ministry of Business, Innovation and Employment’s Strategic Science Investment Fund; and Andrea Clavijo McCormack was funded by the Royal Society Fast Start Marsden Grant ‘Plant communication in times of rapid environmental change’.
