Preparations of yeast that attracts insect larvae and a virus that makes them sick – that is the researchers' new weapon against insect pests. The yeast raises the caterpillar's appetite and ensures that it ingests the virus. – The method is environmentally friendly, and it is possible to select a virus that is harmless to other animals, says Peter Witzgall from SLU.
Biological control involves three sectors: natural enemies and other useful animals, pathogens and pheromones. Useful animals, as predatory mites or bumblebees are most used in greenhouses. For insect control in outdoor cultures either pheromones (to disrupt insect reproduction) or infectious agents (insect-virus and bacteria) are used.
One problem with infectious agents is that the bug must be in a certain stage of development to become fatally infected, or that the insect must ingest the infective agent in food. Previous attempts to attract insects to contaminated bait using pheromones have not been particularly successful, because pheromones attract fully formed insects, which are less susceptible to viruses than larvae.
What Peter Witzgall from SLU and Alan L. Knight from the USDA now are launching is a much more powerful control method where the larvae, which are more susceptible to pathogens, are tempted to eat an infectious preparation, with yeast. In an article in the Journal of Chemical Ecology, the researchers show that the method works well against codling moth, which is a severe pest in apple orchards around the world. Preparation with yeast, sugar and virus was much more effective than preparations without yeast.
– We hope that our discovery is the starting point for the development of a whole new crop protection technology, which can help us to keep pests under control in both fruit production and other crops, said Peter Witzgall.
That the yeast has a key function in the codling moths existence was entirely unknown until about a year ago, when this was discovered by Witzgall, Knight and a number of colleagues. Yeast proved to be a vital part of the larvae’s diet. Yeast scents have great importance not only when the female chooses where she will lay her eggs, but they also attract the larvae.