Neuroptera have receded among insects since the Cretaceous

21 Apr. (EUROPE PRESS) –

A study of the biodiversity of larvae of the insect order Neuroptera during the last 100 million years determines that they have been losing prominence in ecosystems since the Cretaceous.

Human activity is currently causing a loss of natural diversity that some experts describe as the sixth major mass extinction event in Earth’s history. The insect decline is particularly alarming: Insects are not just a very diverse group of creatures in and of themselves, They are also of enormous ecological and economic importance.

The extent to which the insects are disappearing can only be described as exceptional. Therefore, to better understand the underlying processes, it is worth delving into past extinction events: some groups of insects gained in importance and diversified, while others passed by and were forced to retreat to the few remaining niches.

This last point seems to have been the case for the neuroptera, whose modern representatives include lacewings and antlions. Researchers have long suspected that the importance of this group of insects has tended to decline since prehistoric times. Until now, however, there had been no quantitative validation of this hypothesis.

Now, a team working with LMU (Ludwig-Maximilians-Universität München) biologists Professor Carolin Haug and Professor Joachim Haug have published a study in Scientific Reports documenting the diversity of neuroptera from the Cretaceous period to the present day. . For the first time, statistical analysis supports scientists’ view of these insects throughout evolutionary history.

But how do we measure and compare the biological diversity of insects during the process of evolution? At best, we can only paint an incomplete picture of a small fraction of the biodiversity that prevailed in ecosystems of the past, because insect fossils are so rare. And while Jurassic Park may have fueled expectations to the contrary, DNA for use in parentage analysis can no longer be extracted from creepy crawlies encased in amber during the Cretaceous period, informs the LMU in a statement.

Neuroptera are holometabolous insects whose larvae differ considerably in appearance and lifestyle from adults. While many neuroptera pollinate flowers after metamorphosis, their larvae are often ferocious predators, as can be seen from their strikingly stiletto-like mouthparts. It was precisely these mouthparts of the larvae that became the focus of the researchers’ attention. “Unfortunately, the larval stage is often neglected in such analyses,” says Joachim Haug. “However, larvae in particular often display morphological attributes that we can use as a very informative database.”

The basic idea is simple: the different shapes are a marker of biodiversity. The more different forms of head and stylets present in the larvae of neuroptera, the more ecological functions these creatures assume. It follows that if an exceptionally large variety of head and mouth parts occur in a given geological period, it is reasonable to conclude that these insects occupied many different niches at that time. The principle is valid even if only a few specimens have survived and the relationship remains unclear.

The researchers measured the heads of more than 1,000 larvae, including the nearly 300 fossilized neuropteran larvae known worldwide and 800 specimens still alive today. In this way, they were able to confirm that the diversity of neuroptera larvae has indeed declined over the last 100 million years.

“Although our look at the past is limited to a small sample size and very specific regions around the world, we can detect a greater morphological diversity among the larvae of neuroptera in the Cretaceous period,” says Carolin Haugh. “So it’s likely that actual diversity was substantially higher in the past.” However, the big picture of neuropteran history is complex: while their diversity as a whole has definitely declined, some lines of neuroptera have diversified and thus gained importance.

“Our work also showed how much potential there is in the morphological study of insect larvae,” adds Carolin Haug. “Quantitative morphology can reveal changes that cannot be recorded quantitatively within a taxonomic framework.”