Locusts that manage to survive long periods of drought by laying eggs that remain open even for years and who hatch only when the humidity level increases. Frances Duncan, professor at the University of the Witwatersrand School of Animal, Plant, and Environmental Sciences talks about it in The Conversation.
The discovery was made in some provinces of South Africa which, just recently, experienced very long phases of acute drought, the last one lasting seven years and starting in February 2013.
Farmers and ranchers, in addition to being literally devastated by this very long phase of drought, however, had to face, immediately after the end of the drought period, in October 2020, even invasions of locusts. The question is therefore spontaneous: how did the locusts manage to be born and grow and reproduce in a very short time immediately after the end of the dry phase, a phase during which the rain is practically never beaten?
The researcher was mainly interested in the provinces of Northern Cape and Eastern Cape, two of the most affected by drought and by locust invasions, and examined the Locustana pardalina, also known as “brown locust”. It is a species of medium-sized locust endemic to the South African area that usually aggregates in huge swarms that can exist, before becoming extinct, even for several years.
The female of this species can lay, on average, up to 380 eggs contained in 6-10 pods. The eggs are laid in the ground and the pods themselves have a kind of foam “plug” that ensures that the eggs are not too affected by drought. They can in fact remain in this state, in stasis in the ground, until the humidity level outside rises.
At that point, when the first rains begin to fall, they all begin to hatch together and then form huge swarms.
Some of the same newly born locusts, then, produce particular pheromones through the feces that stimulate the other locusts to aggregate and therefore develop the so-called «gregarious phase» and therefore the enormous swarms. These swarms, when they have not yet become huge, may not be detected due to the low human population in these areas of South Africa and this contributes to an exponential enlargement of the same swarms.
In fact, in many of the eggs, as the scientist himself has verified, the development of the embryo begins as soon as the humidity level outside seems to be more favorable. The embryos seem to be able to reduce their development speed, almost to a halt, if the conditions outside are not favorable in terms of humidity level. The stage where the embryo stops developing can last for years.
Notes and insights
- Brown locusts have survived a long drought in South Africa – here’s how (IA)
- Brown locust – English Wikipedia (IA)