The discovery of insect pollination in amber from the Cretaceous period is a remarkable breakthrough that has provided scientists with the first-ever evidence of pollen transport and social behavior in tiny insects. This finding, dating back to 110-105 million years ago, is a significant contribution to our understanding of the co-evolution between insects and plants. The study, published in the Proceedings of the National Academy of Sciences (PNAS) in May 2012, was the result of an international team of scientists from various institutions, including the Instituto Geológico y Minero de España, the University of Barcelona, the Muséum national d’histoire naturelle, the Smithsonian Institution, and the European Synchrotron Radiation Facility (ESRF).
The amber samples used for this study were collected from the Basque Country in Northern Spain, where numerous Cretaceous-era amber deposits have yielded a wealth of information about the evolution of life during that time. These samples revealed an astonishing array of insect fossils, including several specimens of thrips, tiny insects that are less than 2 millimeters in length. The findings of this study, particularly the discovery of thrips covered in pollen grains, represent the oldest known record of pollination by insects. More specifically, these thrips belong to a newly described genus called Gymnopollisthrips, which contains two newly identified species, G. minor and G. major.
Pollination is a process central to the reproduction of many plant species, with over 80% of plant species relying on animals, particularly insects, to transport pollen from male to female parts of flowers. While the most well-known pollinators today are bees, butterflies, and moths, many other lesser-known insects, such as flies, beetles, and thrips, also play crucial roles in this process. Over millions of years, these insects have evolved in close relationship with plants, transferring pollen as they feed on nectar, pollen, or other plant tissues. In return for this service, the insects are rewarded with food, such as nectar or pollen.
The discovery of fossilized thrips with pollen grains attached to their bodies provides compelling evidence that this mutualistic relationship between insects and plants existed long before the rise of modern flowering plants. In fact, the amber samples from the Cretaceous period indicate that thrips were likely among the earliest groups of pollinators in the history of the Earth. This discovery offers a glimpse into the early stages of the co-evolution of flowering plants and their pollinators, a relationship that would eventually shape the Earth’s ecosystems.
The fossils, which include six female thrips specimens, exhibit specialized hairs on their bodies. These hairs are ringed in structure, a feature that increases their ability to collect pollen. This adaptation is strikingly similar to the specialized hairs found on the bodies of modern pollinators, such as domestic bees, which have evolved similar structures to aid in pollen transport. The specialized hairs of the thrips, along with their ability to carry pollen, suggest that these tiny insects were playing a role similar to that of modern-day pollinators. Their evolutionary success in this role is evident in the specialized adaptations that allow them to thrive in their ecological niche.
The research team used cutting-edge technology, including synchrotron X-ray tomography at the ESRF in France, to study the thrips specimens in unprecedented detail. This technique allowed the scientists to create three-dimensional images of the thrips and their attached pollen grains, revealing the distribution of the pollen on the insects’ bodies at very high resolution. The results of this analysis provided further evidence of the thrips’ role in pollination and their close interaction with plants.
The pollen grains found on the thrips are very small and exhibit characteristics that make them highly adhesive, which is essential for their transport by insects. The pollen itself has been identified as coming from a species of cycad or ginkgo tree, both of which are ancient groups of plants that have been around for millions of years. Ginkgo trees, in particular, are living fossils, with only a few species remaining today. These trees have separate male and female individuals, with male trees producing pollen cones and female trees bearing ovules, which develop into seeds after successful pollination. The discovery of this pollen suggests that thrips were involved in the pollination of ginkgo trees, transporting pollen from male cones to female ovules, where it could fertilize the ovules and produce seeds.
One of the most intriguing aspects of this discovery is the question of why the thrips were collecting and transporting ginkgo pollen. The researchers suggest that the thrips’ specialized hairs and their behavior of transporting pollen cannot have evolved purely as a benefit to the ginkgo trees. Instead, it is likely that the thrips were seeking the pollen as a food source for their larvae. This theory suggests that these thrips formed colonies in which the larvae were sheltered and protected inside the ovules of the ginkgo trees. The adult female thrips would transport pollen from the male trees to the female ovules, pollinating the trees in the process while simultaneously feeding their larvae.
The discovery of these fossilized thrips and their pollen grains provides the oldest known direct evidence of insect pollination, shedding light on the origins of this vital ecological process. Amber, which is fossilized tree resin, is a unique and invaluable material for studying ancient life, as it can preserve intricate details of organisms and their behaviors over millions of years. The preservation of behavioral features, such as pollination, is one of the reasons why amber is such an important resource for paleontologists. It allows scientists to observe the interactions between ancient plants and animals in remarkable detail.
This discovery also provides valuable insights into the evolutionary history of plant-pollinator relationships. Around 100 million years ago, during the Cretaceous period, flowering plants began to diversify, gradually replacing conifers as the dominant plant group. Insects, such as thrips, played a key role in this transition by pollinating the early flowering plants, ensuring their reproductive success and contributing to the rise of the diverse plant life that we see today. The co-evolution of plants and pollinators is one of the great evolutionary success stories, and this new fossil evidence offers a window into its early stages.
Carmen Soriano, who led the investigation of the amber specimens with X-ray tomography, remarked on the significance of the discovery. “This is the oldest direct evidence for pollination, and the only one from the age of the dinosaurs. The co-evolution of flowering plants and insects, thanks to pollination, is a great evolutionary success story,” she said. The discovery not only highlights the role of thrips as early pollinators but also reinforces the idea that the mutualistic relationship between insects and plants played a crucial role in shaping the Earth’s ecosystems.