Impacts of GM plants on natural enemies

Science programme: Gene-based insect science

Natural enemies are organisms that feed on or use other organisms for their livelihood, often killing them in the process. Examples are predatory beetles that consume their prey and parasitoid wasps that lay their eggs and develop inside their hosts.

Natural enemies play an important role in ecosystems by regulating the population levels of their hosts. There is often a balance between predator and prey populations that can prevent the prey species from over-utilising its resources in outbreaks and experiencing population crashes.

Humans have introduced natural enemies into crops around the world as biological agents to control pests and as components of integrated pest control systems. Pest control by natural enemies can have the beneficial effect of reducing the need for pesticide application in crops. Many pesticides indiscriminately kill both pests and natural enemies.

If GM plants harm natural enemies, imbalances could occur in ecosystems and pest control in crops could be disrupted. GM plants could have indirect effects on natural enemies if prey were fewer, smaller, less nutritious or behaviourally unacceptable. Direct effects could occur if the protein expressed in the GM plant was toxic to the predator and the predator consumed enough of it to be harmed. This could potentially occur if a predator eats plant material in the gut of its prey.

Our team has carried out contained laboratory experiments to study the impacts of GM insect-resistant plants on a native predatory beetle.

Tobacco is used as a "model" plant because it is easy to genetically modify and it grows quickly, providing ample leaf material for experiments. The GM plants express either a protease inhibitor (PI) that disrupts insect digestion, or a biotin-binding protein (BBP) that prevents larval insects from moulting.

The prey is the common cutworm, Spodoptera litura, a widespread international pest of many crops. The predator is the native (endemic) ground beetle, Ctenognathus novaezelandiae, a generalist predator that lives in coastal lowlands, particularly in podocarp and broadleaf forests, pine plantations and sand dunes.

Prey caterpillars were fed only on either "control" non-transgenic tobacco or GM insect-resistant tobacco expressing either the PI or the BBP.

Predator larvae were fed from egg hatch for 90 days and newly-emerged field-collected predator adults were fed for 280 days on an exclusive diet of PI, BBP or control-fed prey.

There were no impacts of the GM plant-fed prey on larval feeding, growth or survival or adult feeding, growth, survival or fecundity (eggs laid).

Ongoing studies will look at effects on the next generation and will use mixes of GM-fed and field collected prey.