It happened in Southeast Asia. Millions of farmers there earn their living growing cassava. It grew without the help of pesticides. Then the mealybug came and ravaged the crops. The impact was terrible. The price changes affected the entire surrounding economy. The solution? Bring in the cochineal enemy. Millions of mealybug parasitic wasps were introduced, reversing the havoc in just a few years. When humans introduce new species into ecosystems, sometimes it works … and sometimes it doesn’t.
This type of intervention is known as classical biological control. A natural predator is supposed to stop a pest from spreading. “Biological control has been the norm for millennia,” says Rose Buitenhuis. She is a researcher at the independent horticultural science organization Vineland Research and Innovation Center in Canada.
For the people of pre-Columbian Mesoamerica, cane toads were a powerful ally for keeping pests that destroyed crops at bay. They were received in grain fields and storage yards. But the cane toad is hated in Australia. Why? It was imported from America as an organic control in 1935 and thrived in sugarcane crops in its new environment. But everything got out of hand. In 2007 it was estimated that the cane toad covered approximately 1.2 million square kilometers of Australian wilderness. Predatory populations collapsed, species that died from the poison of the cane toad. Every year millions of toads are removed by the Australian government and local activists.
There are at least ten cases of biological controls that have become invasive species throughout history. During World War II, Japanese and Allied forces released mosquito fish. They feed on mosquito larvae. They wanted to reduce the spread of malaria among troops in the Pacific islands. Now an invasive species in the area where it quickly dispersed and exceeded the number of local species. The same applies to the Asian ladybird in Europe, which was introduced to control aphids.
There are basically three types of bio-controls: predators, parasitoids, and pathogens. Cane toads are an example of predatory biological control. They feed on the cane beetles, but are unfortunately not too demanding. And they began to hunt other native insects that were not pests. Parasitoids are a little more nasty. They only lay their eggs in caterpillars or beetles so that the resulting larvae can emerge from their host’s belly … and kill them in the process. Pathogens can appear in the form of fungi, viruses or bacteria that kill the host or render it sterile. These tend to be used against very specific types of pests.
When humans introduce new species into ecosystems, there are always risks. In recent years, however, the popularity of organic controls has expanded to other sectors such as flower growing, viticulture, and outdoor fruits such as strawberries.
In Canada, 92% of flower growers use organic control as their primary pest control strategy. It’s an amazing success story that came about because of its resistance to pesticides.
The exclusive use of chemicals does not seem to be a sustainable long-term strategy. Let’s just hope that no new accidents happen.