© Jurriën van Deijk
As it currently stands, the trees where the caterpillars are found are usually sprayed. However, Jurriën van Deijk of the Vlinderstichting (‘Butterfly Foundation’) thinks that a different approach should be feasible. An approach in which nature is left to its own methods, instead of using poison. ‘An oak like that is an ecosystem of its own, with a huge biodiversity. When you spray it, you kill many species that live on and in it, not just the oak processionary caterpillars.’
Earlier this year, Van Deijk and his colleagues have sown road verges on eight locations in the province of Gelderland. The researchers also placed various insect traps in the trees. ‘The aim is for the flowers to attract more insects, including the oak processionary caterpillar’s natural predators, such as ichneumon wasps, ladybug larvae and red ants.’
A sown road verge. © Jurriën van Deijk
Lacewings play a particularly important part in the natural control of the caterpillars. The larvae of the lacewings consume the eggs and larvae of the oak processionary, as well as the caterpillars themselves. A grown lacewing consumes nectar and can even survive winter. A sufficient number of flowers in spring might thus ensure that the larvae of the lacewing will control the numbers of the caterpillars. Van Deijk: ‘In the current situation, we are often acting after the fact by fighting the caterpillars once there is already an infestation.’
The test will last until the end of next year. According to the researchers, if the blooming road verges turn out to function as expected, it will mean that this method is both a cheaper and more sustainable alternative to spraying or sucking away caterpillars. Van Deijk: ‘We hope that blooming road verges will create a system that keeps itself balanced. An additional advantage is that it all looks beautiful.’