Science - December 13, 2012

Livestock seeks natural enemy of vampire mite

Can the red mite be controlled using predatory insects? Growing interest in biological pest control in livestock sector.

It may e possible to control the destructive red ite using its natural enemies.
Horticulturalists have been making large-scale use of biological methods of controlling pest insects for years, but the livestock sector has hitherto taken a more conservative stand. The odd pig farmer has used ichneumon wasps to keep the flies down, but most pests in livestock barns are controlled chemically. Times are changing though. The rules for applying chemical substances have been tightened up, and many of the pests are becoming resistant to the chemicals anyway. So the livestock sector now wants to follow the horticulturalists' example and start using biological pest control instead of pesticides.
Eureka moment
First in line is the red mite (Dermanyssus gallinae), also known as the poultry or roost mite. Thea van Niekerk of Livestock Research is involved in research on the natural enemies of this persistent little vampire, the plague of the poultry farm. It causes anaemia and, in extreme cases, death in laying hens. When night falls and the hens go to roost, this mini-Dracula crawls out of the woodwork in search of chicken blood.
Amsterdam biologist Maurice Sabelis's group has identified two predatory mites whose menu of choice includes the red mite. The Amsterdam team worked together with Livestock Research on a laboratory test to find out how well these predatory mites do their job. In well-sealed cages - nothing was to be allowed to escape - three chickens were kept company by 300 red mites and 1000 of their natural predators. At the end of the trial, the predatory mites had devoured many but not all of the red mites. They seemed to have difficulty tracking down all of their prey. The same problem was observed when the test was transferred to the barn. After some time, the researchers could not find the predatory mites anymore, whereas there were still red mites present. 'The predatory mite does not manage to hold its own; you have to bring in new ones frequently,' says Van Niekerk. 'We haven't found reached the eureka moment yet.' The Amsterdam team wants to create hiding places for the predatory mites on the route taken by the red mites to the chickens, to increase their chances of success.
Fungi
Van Nierkerk's research is part of a package of three projects aiming at combatting the bloodthirsty red mite. The second project is in the hands of Wageningen entomologists. Their 'attract-and-kill' approach is to lure the red mite into a trap and kill it with fungi. This approach has been copied from Wageningen malaria research, says entomologist Sander Koenraadt. A species of fungus used to kill malaria mosquitoes in Africa also appears to be helpful for controlling the red mite, but Koenraadt still needs to identify the most effective species for the job. The choice of lure proved more complex. 'We have found a few aromas, but you need a mix of different aromas.' And that is as far as the research will get for now, as an application for follow-up funding to the STW technology foundation two years ago was rejected. 'I really want to go on, but we don't have funding for follow-up research right now.' 
Alarm system
The third part of the package is a study led by Monique Mul of Livestock Research. She is developing an alarm system that warns the farmer when the number of red mites in a barn exceeds a certain level. This is important because the predatory mites work best when they go into action at the beginning of an outbreak. The same goes for the commonly used chemical pesticide silicon powder, so as long as there is no alternative, Mul's system can help chicken farmers to keep the amounts they use to a minimum, at least. The second prototype of Mul's metre is almost ready. If there is a company that wants to develop the sensor further and market it, this will bring biological control of the red mite one step closer.

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