(ORDO NEWS) — Australian bogong armyworm numbers, which fell by 99.5 percent due to the 2017-2019 drought, have begun to recover thanks to a three-year period of heavy rains.
According to The Guardian, this year, entomologists note significantly more of these butterflies than in previous years.
This is good news for Australian ecosystems, including the rare mountain couscous that feed on cutworms. However, the population of the species is still under threat.
Many once numerous species of insects have fallen into decay due to the fault of man.
For example, the North American population of monarch butterflies (Danaus plexippus plexippus), which are well known for migrating to Mexico and California every year for wintering, has declined so much that it has been given the status of endangered.
The main threats to these Lepidoptera are considered to be the disappearance of food plants for caterpillars, excessive use of pesticides and climate change.
And the North American locust (Melanoplus spretus) completely died out by the beginning of the last century due to plowing of the prairies and grazing.
A similar story happened with the Australian bogong cutworms (Agrotis infusa). At one time, about four billion of these butterflies lived in southern Australia.
They bred on the plains from Queensland to Victoria, and traveled to the Southern Alps in the summer to wait out the hot months, resting in cool caves and crevices (it should be noted that there are sedentary populations of this species).
These insects migrated at night, overcoming about a thousand kilometers in one direction. Sometimes during flights they formed huge clusters that obscured the moon.
However, since the 1980s, the number of bogong cutworms began to decline. It fell especially sharply in 2017-2019, when Australia had record high temperatures and almost no rain.
Due to the drought, the caterpillars of the butterflies could not find enough food, and the adults experienced heat stress in the caves where they gathered for summer vacations.
As a result, according to entomologists, the number of cutworms has decreased by 99.5 percent from the original.
In many mountain caves, where researchers have noted millions of these butterflies before, they are almost gone.
In 2021, the International Union for Conservation of Nature has given this species the status of endangered.
The decline in the number of bogong cutworms has become a major problem for Australian ecosystems. The fact is that many local mammals, birds, reptiles and other animals ate these insects.
In addition, the scoop during their rest in the mountain caves was traditionally collected and eaten by the Australian Aborigines.
Butterfly declines have hit the mountain cuscus (Burramys parvus), the only marsupial that hibernates, the hardest. Bogong scoops make up to a third of the diet of these animals.
It is not surprising that couscous, which had previously been considered a rare species, began to disappear after the butterflies.
In 2018-2019, about half of the females of these marsupials were unable to raise offspring, and in some areas this proportion reached 95 percent.
Fortunately, the last three years in Australia have been extremely rainy due to the natural La Niña phenomenon.
As a result, conditions on the local plains became more favorable for Bogong cutworms, which allowed them to partially restore their numbers.
Entomologists note that this year they see a lot more of these butterflies than in drought years.
Although the species remains low overall, in some places it has already reached the levels that were observed before 2017.
Thanks to the increase in the armyworm numbers, mountain couscous also received a little respite. These marsupials are still very few, but zoologists report that their situation has improved slightly.
Despite the positive news, experts warn that the future of bogong scoops and their dependent species is still at risk. It took three whole years of intense rains for these insects to begin to re-emerge.
This shows how hard the drought has hit them. At the same time, anthropogenic climate change makes it more likely that such hot and dry periods will recur in the future.
However, it is hoped that, due to abundant rainfall, the armyworm population will increase for at least a few years.
Recently, entomologists have found that these moths move in a straight line, adjusting their flight direction and altitude depending on which way the wind is blowing.
Most likely, dead heads have an internal compass. Perhaps they are guided by the landscape and the Earth‘s magnetic field.
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