Welcome Hester Williams
Hester Williams
We are very pleased to introduce a new PhD student, Hester Williams, who is based at Landcare Research in Lincoln. In 2007, South African-born Hester and her husband moved to Canada, but are now pleased to have settled in Christchurch where they have close relatives. Hester has been awarded a scholarship through Auckland University and the Ministry of Primary Industries to develop strategies to eradicate invasive insect species at the early stage of invasion.
The idea behind her research is that biocontrol agents released in New Zealand can act as a proxy for invasive insects. “Sometimes insects arrive in New Zealand unintentionally but the factors that govern whether they establish and how quickly they spread have rarely been studied under field conditions,” said Hester. “Basically I will be looking at why small populations of certain species do not establish. Apart from environmental factors, there may be other intrinsic factors that affect population growth or make it difficult for small populations to survive (Allee effects), such as genetic diversity, that can affect establishment in a new country,” explained Hester.
The early stages of establishment are critical but more often than not we don’t get a chance to study newly established insect pests because they go undetected until they are widespread. By this time, eradication can be very difficult. Some of the factors affecting the establishment of newly arrived insects include the presence of predators and competitors, environmental conditions, host-plant quality, and the age structure and genetic diversity of the founder population.
“By using a range of field experiments I hope to show which factors and conditions are the most likely to result in establishment of founder populations,” said Hester. “Ironically, once the populations have established, I will be looking at methods to eradicate them using techniques that will lower the population level to a critical level (below the Allee threshold where the population will go extinct). This can be done, for example, by removing a proportion of the host plant, altering the host plant distribution to create a fragmented resource or by manipulating predation rates,” Hester said.
Although the finer details of Hester’s studies are still to be decided, it is likely she will use biocontrol of tradescantia (Tradescantia fluminensis) as a model system and look at the key factors that affect establishment and extinction of small founder populations of the beetles that have recently been introduced as biocontrol agents to manage this plant. “One of the things that makes tradescantia a good host plant to work with is that the agents are not yet widespread – so it is still possible to find areas that are not under attack to conduct experiments,” Hester added.
In addition to these experimental approaches, Hester will also undertake a detailed quantitative review, using data mining, of the successful and failed releases of biological control agents, to identify the key factors that could be used to predict successful and unsuccessful ‘invasions’ and cases where temporary establishment occurred but agents subsequently went extinct.
Hester is not new to the field of biological control and spent the early part of her career working as a biocontrol researcher at the Plant Protection Research Institute of the Agricultural Research Council in Pretoria, South Africa. Much of her work focused on the biocontrol of lantana (Lantana camara) and cat’s claw creeper (Macfadyena unguis-cati), an invasive climber from South America. Both of these plants are in New Zealand as well, and while lantana is already the focus of biocontrol in New Zealand, cat’s claw creeper is classified as an unwanted organism and is expected to become a more widespread problem in New Zealand in future. She might well come across these old enemies at some stage in New Zealand. “At the start of my career, I couldn’t decide whether I preferred working with plants or animals but as it turned out I got to work on both!” said Hester jokingly. “But what I enjoy most is the combination of field and lab work,” she added.
Hester’s PhD project is part of the new ‘Urban Eradication’ programme funded by the Ministry of Business, Innovation and Employment (MBIE) programme. Hester is being supervised by Darren Ward and Mandy Barron (Landcare Research) and Ecki Brockerhoff (Scion).