Thrips In Fossil Evidence

Amber is a hard resinous material made from tree sap. I have discussed its formation in a previous post. In 2009, amber deposited around 100 million years ago was found in the North Coast “Basque” area of Spain. The amber has numerous “bioinclusions” including tiny insects that are preserved in fine detail. Study of these fossils provides clues about life on earth 100 million years ago and helps to reconstruct the history of life on earth.

Pollination of plants by insects is an important feature of our ecosystem. The earliest plants were not insect pollinated. There is interest in reconstructing how pollination first evolved. A recent report in PNAS describes thrips with grains of pollen attached to hairs on the wings and body reminiscent of the hairs on extant pollinator species. These Thrips are the earliest known pollinators. Thrips as ancient pollinators is interesting because pollination is not associated with modern thrips.

Pollen grains are unique to the plant species that produces them and can be used to identify the plant. In this case, the pollen on the thrips is similar to pollen found on Ginkgo trees. Why did the thrips develop hairs for transporting pollen? The authors speculate that the thrips transported pollen from male Ginkgo trees to provide additional nutrients for their larvae in flowers of the female Gingkos. Pollen is much higher in protein than other plant tissue and would promote development of the larvae. Ginkgos have male trees with pollen and female trees with flowers but no pollen. The absence of pollen makes Ginkgo flowers less nutritious than flowers of other plants. Pollen transport by adults to feed their larvae would be a useful adaptation for feeding on Ginkgo. Even though the Ginkgo suffers some damage by feeding thrips, the pollination services may have been a net benefit to the plant.

Studies of modern pollinators reveal that both the plants and the insects benefit from their interactions. The plants gain by increasing the probability that their pollen will find a flower and produce more offspring. The insects gain more nutrition that increases the number of their offspring. Pollination is a winner for both insects and plants.

Pollen grains from 100 million years ago attached to fossil thrips.
Image: Penalver et al.
http://www.pnas.org/cgi/doi/10.1073/pnas.1120499109

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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