Human influence may have a role to play, say scientists
Human activities are likely making modern insects more voracious than their ancient counterparts, according to a new study.
Researchers arrived at this by comparing insect damage on modern plants (post 1995) with fossilised leaves from the Late Cretaceous period (nearly 67 million years ago) through the Pleistocene (2.06 million years ago).
“The difference in total damage frequency in modern plants is more than double of the fossil record,” Lauren Azevedo-Schmidt, a postdoctoral research associate at the University of Maine, told Down To Earth.
The increase in damage was more likely caused by all groups of herbivorous insects and not just one group, the study published in the Proceedings of the National Academy of Sciences showed.
Azevedo-Schmidt and her colleagues studied leaf damage by examining patterns left behind by insects on leaves after they were eaten.
The patterns vary as different insect groups have specific mouthparts. For example, Azevedo-Schmidt said that an insect with a powerful mandible or jaw, like a grasshopper, can eat leaf tissue and veins.
An aphid, on the other hand, makes only a tiny hole with its needle-like mouth, she explained.
“These patterns vary in size and shape and are preserved on fossils and modern leaf tissues,” the expert said.
The researchers observed a sharp increase in damage frequencies in modern leaves.
Among the fossil leaves, the youngest dates back to 2.06 million years ago. This predates early human migration from Africa roughly 1.75 million years ago.
As data on the more recent Pleistocene (1.8 million-10,000 years ago) and Holocene (11,650 years before the present) were not part of the study, the researchers could not map out exactly when levels of damage to leaves increased.
Based on data on modern leaves, the researchers speculate that humans may have influenced the insects’ ability to cause damage within modern forests.
“The most human impact occurred after the Industrial Revolution,” the researchers wrote in the study.
Further, preserved plant samples from the early 2000s were 23 per cent more likely to have insect damage than specimens collected in the early 1900s, the paper noted.
This pattern can be linked to climate warming, the researchers speculated.
But, they added, other factors such as urbanisation and the introduction of invasive species could have also played a part.
This increase in insect-driven plant damage is occurring despite reports of insect decline, the study pointed out.
A 2019 analysis showed that 40 per cent of insect species were faced with extinction threats.
Habitat loss, pesticides, agrochemical pollutants, climate change and invasive species were cited as possible reasons for the decline.
Azevedo-Schmidt is unsure of how climate change drives both declines in insect abundance and an increase in insect appetite.
She pointed towards two theories that could explain this dichotomy.
“Insect damage comes down to food consumption and insects needing to eat enough to get the nutrients they need,” Azevedo-Schmidt explained.
The warming climate and increasing carbon dioxide levels reduce the levels of an essential nutrient — nitrogen.
“Because of this, insects need to eat more leaf material to get the same amount of nitrogen that they would have received in a cooler world,” she explained.
Alternatively, climate change could create conditions ripe for a specific group of insects to thrive.
“These same insects could be making more of the same type of feeding damage,” she said. Future studies, she added, can provide concrete answers.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
.png)
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.