Until recently, controlling aphids caused Christiaan Bot, production manager at Arend Roses in Maasland, a lot of headaches. Although he is familiar with biological methods, aphids were still treated with chemicals. However, the effectiveness of the chemicals was deteriorating rapidly, so Christiaan switched to the gall midge Aphidoletes, which turned out to be successful.
“Until two years ago, we used to spray against aphids about once a fortnight, but as time went on aphids reappeared more and more quickly. None of the chemicals currently permitted work well,” according to Christiaan. “In the past, I’ve tried to combat aphids biologically, sometimes using parasitic wasps (Aphidius). This worked well, but the problem with roses is that the aphid mummies were visible on the stem when the flowers were harvested. Although these mummies are entirely natural, it is perceived as a quality problem.”
Marcel Verbeek, consultant at Biobest Netherlands, suggested to Christian that he should do a test with the Aphidoletes gall midge. This midge is a real predator, and leaves no mummies behind on stems. The experiment was successful. Marcel Verbeek says, “The trick is not just using the right natural predator; it is equally important to create the right conditions for this predator. It is crucial for Aphidoletes that it has the right environment to breed in.”
Christiaan managed to create such an environment using buckets of moist coconut substrate, covered with old newspapers. This mimics the natural conditions which are necessary for adult mosquitoes to mate. They then go into the greenhouse looking for infestations of aphids.
Aphidoletes is known for its excellent searching ability. With just 20 buckets, Christiaan managed highly effective aphid treatment on 4 hectares of roses. That translates to just 0.2 individuals per square meter, which seems very little, but enough to give excellent results.
With Aphidoletes destroying aphids, Arend Roses now has a new, highly effective addition to its biological control measures. Christiaan says, “We had already managed efficient biological control of whiteflies, spider mites and thrips, but this is the first time we have found an effective natural remedy for aphids. Now we really have found the missing link for an integrated biological systematic approach.”