War between two tiny critters should save pepper plant and rose
Floriculture, including roses and gerberas, suffers from a tiny insect: the Echinothrip Americanus. Biologist Giuditta Beretta earned her doctorate in natural pest control and investigated the peculiar behavior of this insect. “The insect kept swinging its abdomen back and forth, easily repelling attacks.”
A group of microscopic predatory mites opens the attack. Indeed, on the bell pepper plant, the habitat of these predatory mites, there is an intruder: the pest insect Echinothrip Americanus. The mites can barely be seen with the naked eye. Their invader, on the other hand, at one and a half millimeters long, is 10 times larger. Like a scorpion, the insect swings its abdomen up and down in an attempt to repel the predatory mites. With success! They give up. Meanwhile, the insect sucks out the leaf cells of the bell pepper plant, to the displeasure of the bell pepper farmer.
For Dutch bell pepper farmers, the North American pest insect Echinothrip Americanus is a thorn in their side. But ornamental plant cultivation, with an annual export value of over six billion euros for the Netherlands, suffers the most. This is because the insect causes leaf loss, making plants less able to grow. The use of pesticides turns out to be less and less effective and sustainable.
Biocontrol
That is why research is being conducted worldwide into controlling pests with natural control agents, also known as biocontrol. “Biocontrol is aimed at reducing pests through the use of natural enemies,” explains Giuditta Beretta, who will receive her doctorate on the subject from the UvA on Friday. “These insects can locate pests on the plant or in the soil and then kill or parasitize them. For example, to control spider mites, those spider-like insects that leave a small web on your houseplant, you can buy certain predatory mites such as Phytoseiulus persimilis at a garden center.”
Yet the story is not so simple. Not every pest insect's natural enemy is known, let alone whether it is deployable. Often these natural enemies have a specific preference for certain plants or conditions. As a result, they are not suitable for every crop and may not be effective against a specific insect pest. “It takes a lot of time to find the right natural enemy and test it. In itself, of course, it should not create a new pest,” Beretta stresses.
No success
Beretta's research included studying the natural enemies of the aforementioned E. Americanus. She examined four different predatory mites for their effectiveness. Unfortunately, without success. “A crucial moment in pest control is when the pest is still in the egg stage. Only E. Americanus lays its eggs in the leaf tissue, making it difficult for the attacking predatory mites to find them. In addition, during my experiments, I found that the insect used its abdomen to keep the predatory mites at bay in a special way. Unlike other species, the insect kept swinging its abdomen back and forth persistently, giving the predatory mites no chance to strike successfully.”
Despite the continuing lack of a suitable natural enemy among predatory mites for E. Americanus, Beretta is optimistic. “Once you find the right candidate, it opens up opportunities for more sustainable ornamental cultivation. The use of pesticides is becoming increasingly controversial, even though it is a relatively inexpensive method of pest control. In the long run, natural pest control offers more prospects. When you no longer spray with chemicals, the pollination of crops by bumblebees and other insects can also once again be done naturally, something which is currently done artificially. You can let nature take its course more. But until then, a lot of research is still needed.”
Giuditta Beretta will receive her PhD on Friday 26 January at 11:00 am for her thesis Surviving the greenhouse. Thrips biocontrol, antipredator behaviour and plant-mediated interactions. The defence will take place in the Aula (Oude Lutherse Kerk) and is freely accessible.
