Date:
Author: Sandiso Mnguni, Honorary Research Associate, University of the Witwatersrand
Original article: https://theconversation.com/the-first-fossil-thrips-in-africa-this-tiny-insect-pest-met-its-end-in-a-volcanic-lake-90-million-years-ago-249077
Thrips are tiny insects – their sizes range between 0.5mm and 15mm in length and many are shorter than 5mm. But the damage they cause to crops is anything but small. A 2021 research paper found that in Indonesia “the damage to red chilli plants caused by thrips infestation ranges now from 20% to 80%”. In India, various thrips infestations in the late 2010s and early 2020s “damaged 40%-85% of chilli pepper crops in Karnataka, Andhra Pradesh and Telangana”.
In Africa, a number of thrips species feed on sugarcane and have been known to damage nearly 30% of the crop in a single hectare of a farm. High rates of destruction have been recorded in Tanzania and Uganda on onion and tomato crops.
Now it’s emerged that thrips are hardly new to the African continent and the southern hemisphere more broadly. South Africa’s first and only Black palaeoentomologist, Sandiso Mnguni, who studies fossil insects, recently described a fossil thrips from Orapa Diamond Mine in Botswana that’s more than 90 million years old. He discussed his unique fossil find with The Conversation Africa.
What are thrips and how do they cause damage?
Thrips, also known as thunderflies, thunderbugs or thunderblights, are small, slender and fragile insects. They can be identified by their typically narrow, strap-like, fringed and feathery wings. Over time, they have also evolved distinctive asymmetrical rasping-sucking mouthparts consisting of a labrum, labium, maxillary stylets and left mandible. Most species use these to feed primarily on fungi. Some feed on plants and eat the tender parts of certain crops like sugarcane, tomatoes, pepper, onions, avocado, legumes and citrus fruits, focusing on the buds, flowers and young leaves.
This, along with their habit of accidentally distributing fungal spores while feeding or hunting, makes them destructive crop pests. They tend to feed as a group in large numbers, causing distinctive silver or bronze scarring on the surfaces of stems or leaves.
However, not all thrips are harmful. A small fraction of the 6,500 species that have already been described so far are pollinators of flowering plants; and a handful are predators or natural enemies of moths and other smaller animals such as mites.
fcafotodigital
Tell us about the fossil thrips you’ve discovered
This is the first time that a fossil thrips has been recorded anywhere in Africa – or the entire southern hemisphere.
The Orapa Diamond Mine in Botswana is one of the most important fossil deposits on the continent. It’s about 90 million years old, dating back to the Cretaceous period.
Read more:
Fossil beetles found in a Botswana diamond mine help us to reconstruct the distant past
The deposit is situated 960 metres above sea level in the Kalahari Desert, about 250km due west of Francistown in Botswana, and 824km away from Johannesburg in South Africa. It was first discovered in 1967 and started producing carat diamonds in 1971.
Roughly 90 million years go, steam and gas caused a double eruption of diamondiferous kimberlites. These are vertical, deep-source volcanic pipes that form when magma rapidly rises from the Earth’s mantle, carrying diamonds and other minerals up to the surface. They create a distinctive rock formation that gets studied by geologists. This explosive volcanic eruption formed a deep crater lake at the centre of the mine.
Mining excavations during the 1980s and earlier uncovered and exposed fine-grained sedimentary rocks containing well preserved fossil plants and insects. These have already been studied by many researchers in the past. At the time, geology and palaeontology researchers from what was then the Bernard Price Institute, which has since been renamed the Evolutionary Studies Institute, at the University of the Witwatersrand in Johannesburg, were invited to collect the fossil material.
Although some of the material has been studied in the past, the fossil thrips hadn’t yet been put under the microscope. And that’s just what we did. By using its body characteristics and comparing it to living thrips, we can say for sure that it’s a thrips. But we didn’t give it a formal scientific name because it doesn’t have enough characteristics to classify it at the species level and describe it either as a new species or one that still exists today.
We think that the thrips either flew into the palaeolake that was formed by the volcanic eruption or was transported there through grass from a bird’s nest.
Why is this useful to know?
This discovery sheds light on the biodiversity and biogeography of thrips and many other groups of insects during a time when we know flowering plants that heavily relied on insect pollination were rapidly diversifying. This plant-insect reciprocal interaction goes back to the Devonian period, a time when there was a large super-continent called Gondwana. That’s when the first land plants evolved and dominated the Earth, and inadvertently led to many groups of insects, including thrips, diversifying to keep up with drastic changes in their preferred plant diets and habitats due to the dramatic environmental and climatic changes.
Read more:
Fossil insects help to reconstruct the past: how I ended up studying them (and you can too)
The fossil find also contributes to a more accurate documentation of life on Earth during the Cretaceous and helps scientists in reconstructing the past environment and climate in Botswana.
Hopefully there are more fossil insects waiting to be discovered in Botswana and elsewhere in Africa, to keep improving our picture of this long-ago world, and preserve the heritage of our continent.