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July 18, 2012

Cretaceous insect pollinator and Ginkgo

Reconstruction of a sample of Gymnopollisthrips
on an ovulate organ of an extinct ginkgo.

More than 110 million years ago, in the age of the dinosaurs, a group of insects delivering pollen became trapped in resin beads. An international research team found four female thysanopterans, also called thrips, that had been enclosed in the amber in Álava (North of Spain) for 105-110 million years, with their bodies covered with pollen of gymnosperms.
It is the oldest evidence of pollination discovered so far —and the only one from the Mesozoic Era— that has been presented in a paper published in the journal Proceedings of the National Academy of Sciences (PNAS), May 2012.
One of the females became trapped in the resin when transporting 140 pollen grains, whereas another was transporting 137 grains. These insects are less than two millimetres long and exhibit highly specialized hairs with a ringed structure which had never been seen before and which increases their ability to collect and transport pollen grains. These hairs are very similar to the ones of bees, which have the same function. The study concludes that pollen is from a kind of cycad or ginkgo tree. Only one species of ginkgo trees, Ginkgo biloba, currently survives, which is considered a living fossil.

For which evolutionary reason did these tiny insects, 100 million years ago, collect and transport ginkgo pollen? Their ringed hairs cannot have grown due to an evolutionary selection benefitting the trees. The benefit for the thrips can only be explained by the possibility to feed their larvae with pollen.
Why came these tiny insects of the Cretaceous, whose species was named Gymnopollisthrips by researchers, to thrust in the pollen of plants? The researchteam assumes that this species formed colonies with larvae living in the ovules of some kind of ginkgo for shelter and protection, and female insects transported pollen from the male ginkgo cones to the female ovules to feed the larvae and at the same time pollinate the trees.

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Picture: Enrique Peñalver

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