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In a recent article BBC FUTURE publish about how the tiny parasitic wasp that saved an industry.
What is the news
Scattered among the highly biodiverse forests of South East Asia, millions of farmers eke out their livelihoods by growing cassava. When cassava was first imported to South East Asia from South America . It was able to grow without the help of pesticides. Then in 2008, the cassava mealybug followed the root vegetable to the region and began devastating the crops.
The arrival of the cassava mealybug not only had major impacts on the livelihoods of those who grow cassava. It affected the national economies of the countries in the region and might have had rippling effects elsewhere.
The solution was to find the mealybug’s natural enemy, a 1mm-long parasitic wasp , in its native South America. This wasp is extremely selective about using the cassava mealybug as a host for its larvae.
This type of intervention is called classical biological control. You find a natural predator and introduce it to a crop to curb the spread of a pest.
Cane Toad tragedy
The cane toad is hated in Australia. Imported from the Americas as a biocontrol in 1935, it thrived in its new environment on the sugarcane crops of the northeastern states. The abundance of its favorite prey, the cane beetle, along with other native Australian insects, and the absence of suitable predators meant that cane toad numbers exploded.
In 2007, the cane toad was estimated to cover about 1.2 million sq km of Australian wilderness and number 1.5 billion individuals. Its range is likely to increase with climate change.
The cane toad’s reputation is so poor in the country that the amphibian’s plight has been the subject of ironic children’s books.
As a result of high-profile failures like this, the use of chemical controls – pesticides – instead of biocontrols gathered momentum in the first half of the 20th Century.
The issue with chemical controls
“Chemical controls solved a lot of problems in the 1930s, 1940s and 1950s,” says Buitenhuis. “Farmers didn’t have to work as hard. They could just go to their cabinet, find a spray and the pests would die.”
The issue with chemical controls is that pest species breed quickly, which means that an individual who is resistant to a pesticide can very quickly produce resistant offspring.
The number of pesticides available to farmers is running out. In 2018, three pesticides from a class of chemicals called neonicotinoids were banned outright by the EU having already had their use severely restricted in 2013.
Biological controls
There are broadly three types of biocontrol’s: predators, parasitoids and pathogens. Cane toads are an example of a predatory biocontrol. Parasitoids are a little more gruesome. Often these types of biocontrol are species of parasitic wasp or fly. Pathogens can take the form of fungi, viruses or bacteria that kill or make their host infertile.
Successful biocontrols should have a high reproduction rate, so they can multiply quickly when they detect a pest, be very specific in which species they target and able to seek their prey efficiently. In practice no biocontrol is perfect.
Ways of applying
There are also three ways that biological controls can be applied to a crop: classical, conservation and an augmented approach. The cane toad is an example of classical biocontrol – in which a new species is introduced into the environment. In augmented approaches a pathogen or parasite is introduced to a crop at a key time.
“Augmented control is very popular in the European greenhouse sector,” says Wyckhuys.
Buitenhuis Commented
“In Canada we did a survey in 2017/ 2018, 92% of flower growers use biocontrol as the main pest control strategy.”
It is an amazing success story and came about because of pesticide resistance, especially in Canada.
Buitenhuis says that “persuading countries like Colombia, Ecuador and Kenya to adopt such approaches would be “big wins”.
“It is coming, using chemicals only is not a long-term sustainable strategy.” says Buitenhuis. “
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Source: BBC FUTURE
