Neuroptera: Greater insect diversity in the Cretaceous period

Presently, human actions are causing a depletion of biodiversity which some specialists characterize as the sixth significant extinction event in Earth’s past. The decrease in bugs is exceptionally worrisome: Bugs are not only an extremely varied set of organisms on their own, but they also hold immense ecological and financial significance.

The magnitude of the decline in insects can only be characterized as an extraordinary circumstance. Therefore, it is valuable to investigate previous extinction events to comprehend the fundamental mechanisms better. Why is this important? Because in the past, some categories of insects have flourished and diversified, while others have been surpassed and constrained to occupy the limited remaining habitats.

100 million years of larvae diversity

It appears that this has been the situation for Neuroptera, which includes modern-day insects such as lacewings and antlions. Scientists have believed for some time that the significance of this insect group has dwindled since ancient times. Nonetheless, there has been no quantitative verification of this hypothesis until now.

Recently, a group collaborating with LMU biologists, Professor Carolin Haug and Professor Joachim Haug, have released a study in Scientific Reports that records the diversity of Neuroptera from the Cretaceous era to the current time. Consequently, statistical analysis has, for the first time, substantiated the scientists’ perspective on the evolution of these insects.

Measuring and contrasting the biological diversity of insects during the evolutionary process is challenging. At most, we can only provide an inadequate depiction of a small segment of the biodiversity that existed in previous ecosystems because insect fossils are exceedingly scarce. Furthermore, although Jurassic Park may have led to different assumptions, it is no longer feasible to extract DNA from insects trapped in amber during the Cretaceous era for relatedness analyses.

Form and function

Neuroptera are insects that undergo holometabolism, and their larvae vary significantly in appearance and behavior from their adult counterparts. Although many Neuroptera pollinate flowers after metamorphosis, their larvae are frequently fierce predators, as evidenced by their unique, stylet-like mouthparts. The researchers focused on these mouthparts of the larvae. “Unfortunately, the larval stage is frequently overlooked in such investigations,” notes Joachim Haug. “However, the larvae often possess morphological characteristics that serve as an informative data source.”

The concept is straightforward: Various forms indicate biodiversity. The greater the number of distinct head shapes and mouthparts present in Neuroptera larvae, the more ecological roles these organisms undertake. As a result, if a specific geological period displays an exceptionally wide array of head and mouthparts, it is reasonable to infer that these insects occupied numerous distinct niches during that era. This principle remains true even if only a few specimens have survived, and relatedness remains uncertain.

A complex pattern

The researchers evaluated the size of over 1,000 larvae heads, encompassing nearly 300 fossilized Neuroptera larvae that are recognized worldwide and 800 extant specimens. By doing so, they confirmed that the diversity of Neuroptera larvae has indeed decreased in the last 100 million years.

Carolin Haug noted, “Although our examination of the past is restricted to a limited sample size and particular regions across the globe, we were still able to identify a greater range of morphological diversity among Neuroptera larvae during the Cretaceous period. Therefore, it is likely that actual diversity was much greater in the past.” Nonetheless, the general history of Neuroptera is complex: while their overall diversity has certainly declined, certain Neuroptera lineages have diversified, and thus become more significant.

Carolin Haug further commented, “Our research demonstrates the immense potential of morphological examination of insect larvae. Quantitative morphology can disclose alterations that cannot be systematically documented in a taxonomic context.”