2020 could be one of the record books in terms of apocalyptic news. Besides the usual backdrop of fires, floods, and earthquakes, the plague still persists. And you may have heard about a pandemic. But what really nails the apocalyptic mood is the fact that this year swarms of locusts caused the kind of problems they are famous for.
In a little good news, the same kind of research that could save us with therapies and a vaccine against SARS-CoV-2 could potentially help us against future swarms of locusts. That's because a China-based team of biologists has now identified the chemical that causes locusts to swarm and has shown that genetic engineering can eliminate the reaction.
Lots of evidence
There is nothing particularly exciting about any aspect of research here. Instead, the researchers simply put techniques from different specializations together and then applied them to the subject of swarms of locusts. Locusts are usually solitary animals, but they become immensely devastating when conditions cause them to form massive swarms large enough to be picked up by radar. In addition to changing behavior, swarms of locusts actually look physically different, suggesting that the decision to swarm involves far-reaching changes in a locust's biology.
As with many insects, researchers have long suspected that the changes in this species were likely caused by a pheromone. These small molecules generally act a bit like a mixture of odorous substances – they're small molecules that freely diffuse through the air – and a hormone that makes changes in animals exposed to them. In the past, researchers involved in this type of work looked for small chemicals made by grasshoppers that diffuse into the air. They eventually found 35 of them, and of these, six were more common in swarms of locusts.
The researchers in the new team placed individual grasshoppers in an enclosure with two chambers, one with and one without the chemical. They then measured how much time a grasshopper spent in each of the chambers. One of the six chemicals, called phenylacetonitrile, might be useful in that it appeared to repel locusts; Another, called guaiacol, appeared to suppress some of the behaviors associated with swarming locusts. However, the work focused on something called 4-vinyl anisole (4VA) which was the only chemical that attracted swarming grasshoppers. Critically, it would also attract lone locusts, suggesting that it might help attract them into the swarm.
The researchers found that 4VA production increased as the grasshopper population increased. Additionally, the researchers could induce production by forcing many individual locusts into a single cage.
The researchers then identified the specific parts of the grasshopper's sensory organs that responded to 4VA, and then examined a range of olfactory receptors to identify the one who responded to 4VA. They then used the CRISPR gene editing system to delete this gene from grasshoppers, which showed that the insects that lacked the gene were no longer attracted to it.
It is a trap!
Eventually they placed 4VA on sticky boards and placed them outside before releasing locusts in the area. The sticky boards the chemical was on caught an average of 26 locusts; those without the chemical caught an average of three. 4VA was clearly a major attraction for locusts, even in a relatively normal setting filled with other flavors.
All of this is convincing evidence that 4VA is involved in putting together large swarms of locusts. This doesn't mean that 4VA is the only factor, or that there may not be any other chemicals that alter certain aspects of swarming behavior. In fact, the researchers identified some chemicals that could also affect the swarming. However, the data clearly suggests that disruption of signal transmission by 4VA could disrupt the formation of swarms, and thus much of the destructive power of locusts.
And work offers many ways this disorder could work. Genetic engineering to delete the gene that encodes the receptor for 4VA blocked the chemical's ability to attract locusts, so it might be possible to change swarming behavior by releasing non-swarming insects into the population. 4VA is also working on trapping the animals, and the authors note that they could be dragged to areas that have been treated with pesticides, eliminating the need for widespread pesticide use. After identifying the receptor, scientists could one day develop a pheromone-like chemical that interferes with 4VA's ability to activate the receptor.
And all of this is possible thanks to just one chemical. The researchers involved here will likely investigate a more detailed characterization of the other two chemicals they identified: one that repels locusts and one that alters their behavior.
Nature, 2020. DOI: 10.1038 / s41586-020-2610-4 (About DOIs).