On the trail of bloodsucker evolution: Researchers have discovered the oldest known representatives of mosquitoes in Lebanese amber from the early Cretaceous period. The characteristics of these two male individuals caused a surprise: While only the females of all modern mosquito representatives suck blood, the early Cretaceous mosquito males also had the equipment for biting. The scientists say why they only peacefully sip nectar in today's species now seems puzzling.
They rob us of sleep, give us itchy hives or, worse yet, they can transmit life-threatening diseases: Mosquitoes (Culicidae) are notorious pests. Their parasitic lifestyle is undoubtedly an enormous success: over 3,000 species buzz through many different habitats around the world, some of them en masse. In order to be able to produce eggs, the females of these insects always have to consume a portion of blood. For this so-called hematophagy, they have special mouthparts with which they can pierce the skin of their victims and drain their body fluid. The male mosquitoes, on the other hand, only need nectar meals from flowers for their tasks, which is why they only have comparatively weakly developed mouthparts.
Since when have you been bloodthirsty?
But how and when did the special diet arise in the evolutionary history of this group of insects? It is assumed that the ancestors of mosquitoes fed on plant juices. The ancient mosquitoes then apparently had the opportunity to collect animal body fluids, which ultimately led to the development of an increasingly sophisticated biting apparatus. From certain clues in the genome of today's mosquitoes, it is also possible to draw conclusions about the approximate time of origin of this development: the dates point to the Jurassic period. However, the earliest fossil evidence of mosquito representatives only came from the middle to late Cretaceous period.
The current finds now push the evidence back by around 30 million years, report researchers led by Dany Azar from the Lebanese University in Beirut. These are two amber fossils that come from a site in Lebanon that dates back to the early Cretaceous period. Over 100 million years ago there was a tropical ecosystem there with obviously resin-producing plants. Some creatures from this living world were trapped in the sticky plant sap and eventually transformed into amber fossils. “Lebanese amber is the oldest amber with biological inclusions and is therefore a very important find material,” says Azar.
Surprisingly sharply equipped males
In the current case, it is amber that has preserved two mosquitoes of the same species from the early Cretaceous period. The fossil resin preserved the delicate structures of the insects down to the finest detail, making precise analyzes and comparisons possible. The scientists gave the new species, which also represents a previously unknown subgroup due to its special characteristics, the name Libanoculex intermedius.
As can be seen from the characteristics of the antennae, both specimens are clearly males. Given that today's mosquitoes only tend to suck blood among females, weakly developed mouthparts would have been expected. But the researchers were surprised to find that the males of this early Cretaceous mosquito species had strong and sharp structures, like those known from female mosquitoes. According to the researchers, it can be assumed that this device was used “penetratively” and not just for sipping nectar. In other words: Apparently in the Early Cretaceous mosquitoes - or in this particular species - the males were also bloodsuckers.
This is also known for some representatives of other parasitic insects, the researchers write. But in the case of the many species of mosquitoes, the question now arises as to why this diet no longer exists among males. “For Cretaceous male mosquitoes, blood consumption may have been beneficial to increase their ability to fly and mate successfully, as is the case with today's females. But why this behavior was apparently lost later in the males remains unclear,” the scientists write.
Source: Cell Press, specialist article: Current Biology, doi: 10.1016/j.cub.2023.10.047