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Not such evil Weevils

May 26, 2021

Barro Colorado, Gamboa

Join Brazilian biologist, Bruno de Medeiros, as he explores mysterious trade-offs between plants and their pollinators and why they are important to the Brazilian economy and ecosystems.

The next time you open a bag of rice or a box of mac and cheese, only to discover an invasion of tiny, long-beaked beetles—weevils—consider this: there are more than 60,000 species of weevils in the world, more than all mammal, bird, reptile and amphibian species combined. And even though you can safely eat rice weevils (added protein!) or kill them by storing infested grains in the freezer, this pantry pest causes considerable economic loss worldwide. But thousands of other weevil species are beneficial, pollinating plants from orchids and cycads to date and oil palms, and tying together one of the most beautiful, biodiverse ecosystems on the planet.

“Historically, no one knew how palms were pollinated: for example, until the 1970s it was thought that oil palms were pollinated by wind, but the discovery that they were pollinated by weevils made it a viable crop worldwide,” explains Bruno de Medeiros who is finishing up a postdoctoral Fellowship at the Smithsonian Tropical Research Institute (STRI) and just accepted a new job at the Field Museum in Chicago as the Negaunee Assistant Curator in Pollination Biology.

“Oil palm growers began to import a weevil pollinator from Africa (Elaedobius kamerunicus) that vastly improves the yield, just like fruit tree growers introduce bees as pollinators. This particular story doesn’t really have a happy ending from the point of view of the environment, since large-scale oil palm production enabled massive tropical deforestation. But palms are some of the most abundant trees and their fruits are important ecologically and culturally/economically for global markets and to feed local people everywhere, so knowing what pollinates them, and using that information to build more sustainable systems, is critical.”

Climbing its slender but sturdy stem, Bruno de Medeiros, post-doctoral fellow at the Smithsonian Tropical Research Institute, will examine the inflorescences to see what is pollinating this species of palm (Oenocarpus mapora).

Bruno recently joined a project called Amazon 4.0, to define a Third Way for the Amazon. Brazil is the number one nation in the world in terms of biological diversity, followed by Colombia and Indonesia. In the beginning, efforts to conserve the Amazon focused on establishing protected areas (the First Way), but economic development models emphasized intensive resource exploitation (the Second Way). The Third Way aims to empower people to use local resources as well as using technology to monitor and learn about the environment before it reaches a tipping point in which the ecosystem can no longer sustain itself.

“The idea of the whole initiative is to ultimately build value chains based on products that rely on a standing forest and can generate economic development, said Bruno, “Palms are certainly some of the most useful plants in rainforests in general and in Amazonia in particular.”

Bruno’s role in this project is to help design a mobile lab to do genetic research in the field, but he is also coming up with other ways to use new technology to learn more about biology. The next time you post a photo of a flower on social, you may unknowingly become part of one of Bruno’s experiments.

“I’m using artificial intelligence to recognize insect-flower interactions in a dataset with millions of insect natural history observations from iNaturalist, which will let me estimate how many and what type of insects are visiting flowers, and how many of these insects may be eating the seeds of the plant they visit.”

As an undergrad Bruno worked as an intern at the Museum of Zoology at the University of Sao Paulo with beetle diversity expert, Sergio Vanin (1948-2020). On a collecting trip to Serra do Cipó, in southeastern Brazil, Vanin collected weevils from a group of short palm trees that he thought were all the same species. Then a plant biologist figured out that they were actually two different palm species. Vanin wanted to know if each palm species had its own species of pollinator weevil, so he sent Bruno to find out. They ended up discovering a new species of weevil, and Bruno was hooked by the idea that almost every plant out there—especially in the tropics—is associated with a unique group of insects, and that their relationships tie tropical forests, one of the most beautiful and diverse ecosystems on earth, together.

At the 2020 Entomological Collections Network Meeting Bruno won a Golden Net Award for his own short video documenting 18,000 miles and six different field trips of climbing palm trees to discover their pollinators.

Along the way, he discovered that the most important pollinator of one of the most common trees in the forest in both Brazil and Panama is a weevil that not only pollinates flowers, but also eats the seeds. But why sacrifice your seed to a pollinator? This doesn’t seem to make sense from the plant’s point of view, especially since bees and other palm pollinators don’t eat seeds. In fact, seed-eating pollinators are not thought to be very common in nature, although Bruno suspects that there are more to be found.

The most famous example of a seed-eating pollinator is the fig wasp. Like the palms, towering fig trees feed monkeys, bats and countless other rainforest animals. The relationship between figs and the miniscule wasps that pollinate them is so tight that neither partner can live without the other. Biologists call this a mutualism, and Bruno’s advisor at STRI, Allen Herre, has spent much of his career understanding the connection between wasp species and fig species, one of the hallmark interactions of tropical forest ecosystems.

Female wasps may fly almost 10 miles to find the right species of fig to pollinate. Figs hold their flowers inside the inflorescence (what most of us think of as the fig fruit). Pregnant female wasps carrying pollen from another tree squeeze inside the fig through a hole at the apex of a fruit, losing their wings and antennae in the process. Females spread pollen as they move from flower to flower inside the fruit, depositing eggs in some of the flowers and finally dying when their mission is complete.

Male wasps hatch first and fertilize the females (mostly their sisters) even before the females emerge. Then the males bore tiny holes in the walls of the fig, before they die, having never left the fig. Finally, their pollen-covered sisters crawl out through the holes to go pollinate more figs.

Allen and his collaborators, especially Charlotte Jander, think that the fig trees have a lot of control over this relationship. When cheater wasps (wasps that don’t carry pollen) lay eggs inside the fruit, sometimes the fig tree seems to punish the cheater by aborting the fruit and letting it fall to the ground before the wasps can reproduce.

The good pollinator/bad pollinator, or in this case, the good weevil/evil weevil paradox—why do plants support pollinators that eat their seeds, when they could be pollinated by less-damaging insects like bees—is one of the ideas that gets Bruno out of bed in the morning. On a steamy day in March, he unloads climbing gear from the back of his car on a back street in Gamboa, Panama, getting ready to head down into the forest behind Allen Herre’s house. Allen comes out for a moment to say hi and to remind Bruno to watch out for Milagros—but we’ll get to that in a minute.

For his doctoral thesis at Harvard, Bruno exposed the evolutionary relationships between a group of weevil species and the palm trees they pollinate in the genus Syagrus. These palms are related to coconut palms and many of them produce edible seeds essential to the diets of forest animals and rural communities. In Panama, Bruno will spend most of his time climbing a common palm called Oenocarpus mapora, which not only produces valuable seeds, but its fibrous stems are important in rural communities as a construction material.

After arranging his gear on a tarp on the forest floor, Bruno picks out his climbing equipment, dons his helmet, walks over to a tree and places two extra-thick loops of rope around its slender stem. He clips his harness to the ropes, puts his foot into a kind of stirrup and ascends, sliding one loop up the stem at a time. The structures that bear the flowers of this palm—the yellow to reddish-brown inflorescences—look like Beyonce’s lemonade braids, gracefully hanging from the area right below the leaves.

One of his goals is to collect and describe the many insects that pollinate this species. He places a large plastic bag over the inflorescence and beats it with his hand, shaking all of the pollinators down to the bottom of the bag. Today, near the end of the flowering season, there’s only one weevil, Anchylorhynchus bicarinatus, first described here at the Smithsonian’s Barro Colorado Island research station in 1981.

He will work with Lourdes Chamorro at the Smithsonian’s National Museum of Natural History to identify as many of the weevils in his samples as possible. Bruno already has 12 new species of weevils to his name, and has a hundred or more in his collection that he suspects will also be new species.

Oh no! Just as Bruno is getting ready to climb another tree, Milagros the deer appears! Rescued from the Panama Canal as a tiny baby by a Gamboa resident, Milagros sometimes silently stalks folks on night walks and errant field biologists, perhaps looking for a handout. And when she receives nothing, she sometimes rushes the offender. Bruno has dealt with Milagros before…he shouts and runs toward her and she slinks away through the undergrowth. She is one of the strangest inconveniences he has run into…usually they take the form of swarming or stinging ants or a scorpion posed to strike on a palm inflorescence. He always wears a helmet, goggles and gloves, to prevent accidents. His scariest field experience happened in Brazil when his field assistant was sick and stayed in the car, and he fell, hanging upside down from his climbing gear for a while until he managed to right himself. “I only had a few scratches, but that could have ended badly if I hadn’t had the proper redundancy in the way I set up the ropes,” he said.

Shimmying up another stem, Bruno places mesh bags over groups of strands to exclude all pollinators from some flowers, and only bees or weevils from others. After two weeks and again after a month, Bruno will find out how many flowers were pollinated by each, how many seeds result, how many of the seeds are eaten by the weevils, and how may seeds were aborted by the plant. He’ll be able to calculate a cost-benefit for the tree…how many seeds is the tree giving up to “pay” the weevils to pollinate. And he will use genetics to discover how far are the insects traveling with pollen (if the pollen came from the same source).

“Pollination of one flower can lead to the reproduction of either the weevil or the plant, never both,” Bruno said.

Like the figs, he thinks that the palms may also somehow be in charge of this relationship they may abort more seeds that have larvae than seeds without larvae—although this remains to be tested. Like the figs, the partners in this relationship may not be able to live without one another, or perhaps they can…Soon Bruno will have the answer, at least for this species of palm.

At the corner of Main and College streets in Enterprise, Alabama, stands the world’s first monument built to honor an agricultural pest: a graceful statue of a toga-clad woman raising a pedestal high above her head, topped by a larger-than-life-sized weevil. Boll weevils (Anthonomus grandis) from Mexico first appeared there in 1915 and soon ravaged cotton crops across the Southern U.S. So why does the sign under the statue salute the boll weevil as a herald of prosperity? In the face of the weevil invasion, farmers in Enterprise quickly shifted to growing peanuts. By diversifying, they avoided the disaster that befell other cotton farmers.

Nature teaches us to be resourceful under pressure, and the result may be new behaviors, and even new species.

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