Functional biodiversity

: Cabbage with companion plants (Centaurea cyanus)

We combine laboratory, green house, and field experiments to study plant-herbivore-parasitoid interactions in cabbage pests. Our aim is to increase functional biodiversity, i.e. to use wild flowers to attract parasitoids into the cabbage field - or to retain them if we release them - to increase natural pest control. By strengthening biological control we can reduce or even eliminate the use of pesticides. Our approach thus increases biodiversity in two ways: directly through the added plants and the organisms that use them as resources, and indirectly through the reduction of pesticides, which always destroy a plethora of non-target organisms.

What is functional biodiversity?

The term ‘functional biodiversity’ is not always used consistently. We mean that part of the total biodiversity that serves a specific function, i.e. in our case that part of biodiversity that contributes to reducing a pest species (biological control). Our approach is to increase the functional biodiversity in cabbage fields by adding specific plant species that help increase the population sizes and/or effectiveness of beneficial insects, which then reduce the negative impact of pest species.

Our study system

: The main species we work with in the lab

We currently study functional biodiversity in white cabbage (Brassica oleracea var. capitata). We focus on the three main lepidopteran pest species of white cabbage in Switzerland: Mamestra brassicae, Plutella xylostella and Pieris rapae. As natural enemies of these pest species we study the egg parasitoids Trichogramma evanescens, T. brassicae and Telenomus sp. and the larval parasitoids Microplitis mediator, Diadegma semiclausum, Cotesia rubecula and C. glomerata.

The three pest species have roughly equal significance as cabbage pest species in Switzerland. Our work focuses on interactions between the egg parasitoids and M. brassicae, for which we have established a year-round rearing, and on the interactions between the larval parasitoids and P. xylostella.

Egg parasitoids lay their eggs into the eggs of their host. For biological control they have the advantage that they destroy the pest before hatching and thus avoid crop damage. From an experimental perspective they have the advantage that their parasitation rate can be readily measured in the field by laying out lab-reared host eggs but the disadvantage that they are extremely small. Trichogramma brassicae is widely used in biocontrol and commercially available. However, it is not a main enemy of our pests in nature. We are therefore also experimenting with T. evanescens and with species of the genus Telenomus that may be more efficient.

Larval parasitoids are considerably larger than egg parasitoids and lay their eggs into host larvae. They therefore destroy the host only when it has already started to cause some damage. From an experimental point of view they have the advantage that their behaviour is easier to investigate but the disadvantage that their parasitation rate is more difficult to determine in the field.

What we study

We address basic and applied questions encompassing general parasitoid biology, parasitoid behaviour, plant-parasitoid interactions and plant-herbivore-parasitoid interactions.

In the laboratory and the green house we try to establish how the different parasitoids’ survival and fecundity (i.e. parasitation rate) are affected by food availability and quality and what plants are attractive and beneficial to them but not to the pest species. The main goal is to identify the best parasitoid and plant species to use for our field experiments and ultimately as biocontrol agents.

In our field experiments we test the efficiency of the organisms identified in lab and green house experiments and we investigate how to most efficiently apply these organisms. We currently focus on planting wild flowers as strips along the fields, as individual plants next to each cabbage inside the field, and a combination of both. We always use single plant species (as opposed to plant mixtures) to gain maximal control and insight. Especially the approach of planting individual wild flowers (‘companion plants’) next to cabbage heads is new and promising.

Apart from their effectiveness for biological control, we also investigate the technical feasibility and the economic impact of different approaches, as these will determine whether the farmers will in the end accept and apply them.

Possibilities for Master theses

There are always possibilities for Master theses on various topics within the project. A Master thesis is always in collaboration with a university professor who serves as official supervisor. The actual work takes place at FiBL under the supervision of Oliver Balmer or Henryk Luka.

Further Information

Project leader:

FiBL project team:

Collaborations:

Felix Wäckers, Lancaster University, UK
Pius Andermatt, Syngenta, Switzerland
Olaf Zimmermann, Julius Kühn Institute, Germany
Bruce MacDonnald, ETH Zurich, Switzerland
Mathias Kölliker, University of Basel, Switzerland
Peter Nagel, University of Basel, Switzerland
Michael Traugott, University of Innsbruck, Austria

Funding:

Bundesamt für Umwelt (BAFU) (2007-2011)
Bristol-Stiftung (2007-2008)
Ernst Göhner Stiftung (2008-2011)
Parrotia-Stiftung (2008-2011)
Stiftung zur internationalen Erhaltung der Pflanzenvielfalt (2008-2011)
Werner Steiger Stiftung (2009-2011)
Spendenstiftung Bank Vontobel (2009-2011)