Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Melissa Kirk’s PhD Work

Melissa Kirk

We are delighted to introduce a PhD student, Melissa Kirk, who is registered at Auckland University and is based both at the university and at our Tamaki office. Melissa is originally from England and moved to New Zealand when she was 12 years old. She has since lived in Christchurch, Blenheim and Dunedin, and is currently living in Auckland. Melissa’s PhD study is investigating the co-evolution of plants and insects in exotic ecosystems in order to gain a better understanding of the successes, and the risks, associated with weed biocontrol programmes.

Depending on their origins and the time since their separation, genetics play a key role in weed biocontrol programmes in three main ways.

  • A match or a mismatch may occur between the target weed and the weed biocontrol agents.
  • Genetic imbalances may occur between the target weed and the agent, where, for example, low genetic diversity of an agent may reduce its ability to adapt over time.
  • There is often adaptation to novel environments and stressors over time, resulting in genetic differences in the plants and/or the biocontrol agents compared to their source origin.

Melissa will use long-established weed biocontrol systems in New Zealand as case studies. “The aim of my research is to investigate how multiple factors, such as genetic diversity, genetic processes (e.g. maternal priming, epigenetic changes), time since separation, phenotypic/genotypic matching, and rapid adaptation can all influence the outcome of biocontrol programmes.”

The first case study will be on nodding thistle (Carduus nutans) and its three insect biocontrol agents: the gall fly (Urophora solstitialis), the crown weevil (Trichosirocalus horridus), and the receptacle weevil (Rhinocyllus conicus). By using common garden experiments and molecular techniques, Melissa will determine if imbalances occur between native and introduced populations of nodding thistle and its biocontrol agents. “Firstly, I will explore the life history traits of nodding thistle and the presence and abundance of the biocontrol agents in different parts of New Zealand,” said Melissa. “Then I will explore the life history traits and genotypes and phenotypes of nodding thistle from New Zealand, Australia and the United Kingdom (conducted at Sheffield University)”. Melissa explains that these nodding thistle populations have had different relationships with their natural enemies over time.

Native nodding thistle populations in Europe have had continuous exposure to these natural enemies, and they have other insect natural enemies that are not present in the introduced range.  The New Zealand and Australian populations were without any natural enemies for decades until three host-specific biocontrol agents were introduced. “The native populations of the agents in Europe could potentially have higher genetic diversity compared to the introduced populations in New Zealand and Australia, and it is possible that these populations have diverged because of a lack of gene flow. The same could be true for the plant populations,” said Melissa. If differences are found, Melissa also plans to investigate how these traits have evolved. “By understanding which factors influence plant–insect interactions, we can make biological control safer and more effective,” Melissa added.

Melissa majored in ecology and statistics for her undergraduate degree and moved into entomology with a focus on invasive species for her Master’s, where she investigated the influence of propagule pressure, source variation, and dispersal capabilities on the establishment of exotic insects. Melissa considers herself an entomologist with an interest in developing her expertise in molecular biology. “I find insect biocontrol agents so interesting, so I’m very excited about having a project in weed biocontrol with a focus on genetics,” enthused Melissa.

Melissa’s PhD project is funded by the Ministry of Business, Innovation and Employment as part of Manaaki Whenua – Landcare Research’s Beating Weeds programme, by the University of Auckland, and by the Centre of Biodiversity and Biosecurity (CBB) Project Fund. Melissa is being supervised by Darren Ward, Quentin Paynter and Thomas Buckley (all MWLR).


Melissa Kirk -