When roles are reversed – all in the name of science!


Posted by Hester Williams @HesterW123

As international trade and travel increases, the arrival of non-native species in new territories has accelerated accordingly. Many of these non-natives are unable to establish, while the establishment of others are so successful that they become major economic and ecological threats in their new environments. To prevent the arrival of non-native species, governments across the world impose different measures, e.g. surveillance programs, quarantine measures, inspections, and restrictions on movement of certain goods.

Biological invasions can be separated into a sequence of phases including arrival, establishment, population growth, and spread. The second phase of the invasion process is critical as this is where the establishment of a small founder population occurs, and where the success of eradication is much higher while populations are small. 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 that time, eradication can be very difficult.

I have just started my PhD, where I will identify the key factors influencing the establishment (and then eradication) of exotic insect species. However, instead of using exotic species, I will use biological control agents as proxy invasive systems.

A reversal of roles! The biocontrol agent thus becomes the foe, and the invasive plant the friend!

Propagule pressure has emerged as arguably the only consistent factor explaining establishment success, while several intrinsic (‘internal’) processes underpin the effect of propagule pressure, namely demographic stochasticity, Allee effects, and genetic diversity. My studies will focus on the invasive plant, Tradescantia fluminensis, and one of its biocontrol agents, the leaf beetle Neolema ogloblini, and through a combination of field and mesocosm experiments, I aim to identify the role these key processes play in the establishment of the beetle. Heartbreakingly, once beetle populations have been established, I will use methods to eradicate them – techniques that will lower the population level to a critical level (below the Allee threshold where the population will go extinct).


Tradescantia leaf beetle (Neolema ogloblini) adult



Tradescantia leaf beetle late-instar larva

But all in the name of science! This project will generate a better understanding of the key factors that affect biocontrol agent establishment and also invasion success of invasive pest species. Ultimately it aims to give guidance on what eradication approaches are more or less promising for particular species.


Hester Williams is a PhD candidate in the School of Biological Sciences, University of Auckland and is stationed with the Landcare Research Biocontrol team in Lincoln, Canterbury. She is interested in invasion processes of both insect and plant species. Hester is supervised by Darren Ward (Landcare Research/University of Auckland) and Eckehard Brockerhoff (Scion), with Mandy Barron (Landcare Research) as advisor. Her studies are supported by a joint Ministry for Primary Industries – University of Auckland scholarship. The project is an integral part of an MBIE program “A Toolkit for the Urban Battlefield” led by Scion.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s