Can flies be bred as gardeners, weeding undesirable pests from the crop? That is what a European Union (EU) research project has achieved, offering hope for farmers battling the broomrape, one of nature's parasites.
© Fotolia, 2012
Over the course of a two-year EU-funded research project, called Biobroom, Slovakian doctor Peter Tóth uncovered the intricate relationship between the broomrape and the broomrape fly, Phytomyza orobanchia, by decrypting the way they involuntarily communicate through chemical language. The larvae of flies live within broomrape seed capsules and feed on seeds within days. Toth found out which chemicals were attracting the fly, and then made synthetic versions. He was then able to attract flies in the field, so they could be deliberately released in fields infested by broomrapes. He believes his work could lead to an efficient, herbicide-free control of parasitic weeds in all vulnerable crops.
Tóth is assistant professor at the Slovak University of Agriculture in the city of Nitra where he teaches in agricultural entomology, weed control and integrated pest management. His project, backed by €166,563 of funding from the EU's Marie Curie Actions fellowship programme, ran from October 2008 to October 2010 at Wageningen University, in the Netherlands.
Tóth is now working on two patents for applications from the research. One will use the reinforced chemical compound bait to trap and redistribute the flies, while the other is for an early warning system that detects when plants are infested, even before they appear above ground. Tóth says he expects the applications will be picked up by farmers across Europe suffering from broomrapes.
Although its blooms can sprout charming violet, amber or burgundy flowers, broomrape is a small noxious weed that attaches itself to the roots of other plants, sucking out their water, minerals and carbohydrates. The broomrape – or Orobanche – does not use chlorophyll, the green pigment critical for photosynthesis in most plants, and depends entirely on other plants for nutrients. Once a host is infested, its growth slows and yield losses can be significant.
Farmers struggle to control the broomrape, whose scaly flower shoots produce millions of dust-size seeds that are easily dispersed, and long-lived. Indeed, they spend most of their life cycle dormant in the soil, sometimes for decades, making them hard to detect. Broomrape has plagued European agriculture for years, although climate change has made it more aggressive recently, Tóth says. "In Slovakia, in particular, many field plots are infested," he points out. "These plants are almost uncontrollable, and it is a real problem in tomatoes, tobacco and hemp crops. In some areas they have stopped growing tobacco and tomatoes."
Tóth's research looked at the intricate workings of the insect-plant interactions. "I wanted to know why the fly is attracted to broomrape," he says. "I found that it is love at first sight. There is a love potion, a special chemical compound emitted by the broomrape."
Tóth then identified, isolated and chemically reinforced the compounds that attract the flies. This was a complicated task given that there are some 200 broomrape species, and each one is using slightly different plant's language to communicate with surrounding environment emitting more than 200 different volatile organic compounds, he explains. Tóth then narrowed it down by finding out the basic alphabet of broomrape's language - the 40 compounds that all broomrapes give off.
But which compounds actually attract the flies? "We checked by asking the fly," Tóth says. That meant testing the compounds by seeing whether the flies, whose antennae had been removed, were drawn to them. He found 12 compounds that were particularly attractive. Based on the three most attractive compounds for the fly he then made synthetic mixtures, which were then used as a bait to conduct mass trappings of the flies. These synthetic mixes are still being perfected, but if they are successfully commercialised, it could offer an environmentally-friendly protection against a crop menace.