As locust plagues continue to threaten food supplies in Africa, Asia and South America, scientists have come up with a discovery that could pave the way to a new approach to tackling swarms of these insects. As they mature, locusts may become solitary creatures or may gather in masses, depending on factors such as environmental conditions. Transition from one form to another can also occur anytime during a locust’s life cycle. According to researchers at the Institute of Zoology of the Chinese Academy of Sciences, it is the chemical compound 4-vinylamisole (4VA) which actually prompts solitary locusts to form giant swarms.
The United Nations Food and Agriculture Organization (FAO) states that between January and July, locusts devastated crops in an area reaching from East Africa to India. Around 11.9 million people in Ethiopia, Kenya and Somalia are already experiencing acute food shortages, while insect swarms are threatening the food security of a further 20.1 million people. Locusts are also on the rampage in South America.
So far, locust plagues have mainly been tackled with pesticides. However, chemicals have to be spread over large areas, potentially polluting the environment and causing harm to other animals, plants and human beings. “China has been battling locust swarms for nearly 2,000 years, having recorded over 800 major plagues of locusts throughout history,” says Kang Le, a professor of entomology and ecology at the Institute of Zoology of the Chinese Academy of Sciences, and President of China’s Entomological Society.
Kang headed the team of scientists who discovered 4VA, a pheromone which is mainly released from the hind legs of migratory locusts and attracts others of the same species, causing them to aggregate. The pheromone is detected by the antennae and odorant receptors of the insects. Kang explains that it only takes a small number of locusts to trigger the formation of gigantic swarms, which he believes is the reason for the rapid speed at which locust swarms spread.
“A locust has more than 100 receptors, and it has so far been found to emit 35 odorous compounds,” Kang reports. “So our team has undertaken a huge amount of tests to find the receptor that matches the compound 4VA.” The pheromone is equally attractive to male and female locusts, and to juveniles and adults. But the scientists in China have found out that as the density of swarms increases, the amount of the pheromone increases markedly. The substance smells sweet to humans. Migratory locusts have already been genetically engineered to lack the olfactory receptor needed for them to be attracted by 4VA, and the mutants have proved to be incapable of sensing the compound.
4VA could be used to combat locusts in a more effective and environmentally friendly way, Kang believes. “We can synthesise the pheromone to lure locusts and trap them in a designated area, and then spray the targeted area with insecticide, therefore greatly reducing the need to mass spray the chemical,” he explains. Leslie Vosshall, head of Rockefeller University’s Laboratory of Neurogenetics and Behavior, in the USA, even thinks it might be possible to create a chemical that blocks the locust’s 4VA receptors, keeping the insects from aggregating and maintaining a peaceful and solitary life instead.
However, Kang points out that more research is needed to see if the pheromone is also effective in other locust species. He refers to preliminary research which has shown that other locusts living in Inner Mongolia and Yunnan Province can produce 4VA, but stresses that locusts outside China yet have to be examined regarding their ability to release or respond to the chemical.
Mike Gardner, journalist, Bonn, Germany