Rare fossil find reveals early evolution of mosquitoes

In amber some 99 million years old, LMU researchers have discovered the oldest known mosquito larva. The Cretaceous fossil comes from the Kachin region in Myanmar and was preserved in excellent condition. Described as a new species of a new genus, it has been given the name Cretosabethes primaevus. It represents both the first mosquito larva preserved in amber and the first immature mosquito from the Mesozoic Era, as only the fossils of adult mosquitoes from this era had previously been found.

More remarkable still is the morphology of the insect: “This fossil is unique, because the larva is very similar to modern species—in contrast to all other fossil discoveries of mosquitoes from this period, which exhibit highly unusual morphological traits that are no longer present in today’s species,” says zoologist André Amaral, lead author of the study published in Gondwana Research and doctoral researcher in Professor Joachim Haug’s team at LMU’s Faculty of Biology.

These oldest known mosquito fossils come from adult insects and were also found in amber deposits about 99 million years old. Due to their morphology, which differs sharply from that of modern species, they are interpreted as representing a distinct group, Burmaculicinae, an extinct lineage within the mosquito group (Culicidae). Cretosabethes primaevus, by contrast, belongs to the Sabethini group, which includes extant species.

The evolutionary origins of mosquitoes have been situated in the Jurassic period about 201–145 million years ago, based on the fossils that have been found to date. Estimates based on molecular phylogenies widely diverge and yield results between the Triassic and the Jurassic.

The discovery by the LMU researchers provides new clues: “Our results provide strong indications that mosquitoes had already diversified in the Jurassic period and that the morphology of their larvae has remained remarkably similar for almost 100 million years,” says Amaral. This calls into question previous assumptions about the early evolution of this insect group, he observes, and affords new insights into its evolutionary ecology.

Like the larvae of extant species from the Sabethini group, the larva of Cretosabethes primaevus is thus thought to have lived in small accumulations of water, such as form in hollows in tree branches or between the leaves of epiphytic plants. For a drop of resin to fall into such a tiny pool of water and preserve an aquatic larva in amber is most unlikely and therefore the discovery is a rare stroke of luck.

Most amber fossils come from terrestrial or flying creatures that lived on or near resin-producing trees. The most common groups of arthropods discovered in Myanmar amber are spiders, beetles, hymenopterans (bees, wasps, and ants), and true bugs (Hemiptera) as well as adult flies (Diptera).