The secret life of weevils: Revealing their vital role as plant pollinators

We often celebrate butterflies, bees, and bats as pollinators, acknowledging their vital role in fertilizing plants by spreading pollen while they feed on flowers. However, there is a diverse group of pollinators that often go unnoticed, even among scientists: long-snouted beetles known as weevils. A recent study published in the journal Peer Community in Ecology delves into the world of over 600 weevil species, some of which have intricate life cycles intertwined with specific plants they help pollinate.

Bruno de Medeiros, the senior author of the study and an assistant curator of insects at Chicago’s Field Museum, highlights how even experts in pollination overlook weevils, and conversely, weevil researchers rarely consider pollination in their work. This preconception has led to a lack of understanding about the crucial role weevils play as pollinators. With approximately 400,000 identified species, beetles are the largest group of animals globally, and weevils constitute the largest subgroup within beetles, totaling around 60,000 species—an equivalent number to all vertebrate animals combined.

While weevils are sometimes regarded as pests due to their presence in pantries, where they feed on pasta and grains, and their historical disruption of the cotton economy in the American South, many species actually benefit plants by acting as pollinators. The study reviewed numerous previously published descriptions of weevil-plant interactions to gain a better understanding of their pollination roles.

In essence, weevils, with their long snouts, deserve recognition for their important contributions as pollinators, challenging our preconceived notions and shedding light on the hidden world of these fascinating creatures.

Weevil Anchylorhynchus bicarinatus, the main pollinator of the palm Oenocarpus mapora, found in Amazonia and Central America. Here we see an adult weevil covered in pollen among male flowers. Credit: Bruno de Medeiros

In the study, the researchers focused on a specific type of pollination interaction known as brood-site pollination. These interactions involve insects that use the same plants they pollinate as breeding sites for their larvae. According to de Medeiros, this type of pollination interaction is associated with high specialization. Since the insects spend their entire life cycle in the plant, they often exclusively pollinate that particular plant. Additionally, the plants rely heavily on these reliable pollinators.

Brood-site pollination can be likened to the relationship between Monarch butterflies and milkweed, where milkweed serves as the sole food source for Monarch caterpillars and the site for butterfly egg-laying. However, brood-site pollinators, such as many weevil species, take this relationship to the next level. They rely solely on their partner plant for both food and egg-laying.

De Medeiros notes that this type of pollination interaction is commonly perceived as rare or unusual. However, the study reveals that there are already numerous documented cases of brood-site pollination involving hundreds of weevil species and plants, with many more likely awaiting discovery.

The close interdependence between these weevils and plants highlights the mutual reliance necessary for their successful propagation. An example cited is the oil palm, which plays a crucial role in producing peanut butter and Nutella. The oil palm industry faced significant challenges until it was realized that weevils found with the plants were their essential pollinators. The misconception that weevils were not pollinators caused unnecessary delays in understanding and leveraging their role in facilitating the growth of industries like oil palm.

Bruno de Medeiros climbing the palm tree Oenocarpus mapora in Panama to study their pollinators. Credit: Tauana Cunha
Bruno de Medeiros covering insect pollinators with a fluorescent power to track their movements in Brazil. Credit: Tauana Cunha

One of the key motivations behind the new study, according to de Medeiros, is to challenge prevailing misconceptions surrounding a group of insects that are often viewed negatively. He emphasizes that these insects, in this case weevils, can actually play a significant role in preserving ecosystems and the products that are important to us.

“We are shedding light on a group of insects that many people consider pests, and we’re demonstrating their potential importance in maintaining the balance of ecosystems and sustaining products that hold value for us,” de Medeiros explains.

The researchers aspire to increase awareness and appreciation for the pollination role of weevils, particularly in tropical regions, by summarizing existing knowledge and offering insights into areas that require further investigation.

“Our intention is to provide a comprehensive overview of what we already know and offer guidance on areas that deserve attention. By doing so, we aim to assist fellow researchers and the general public in developing a deeper understanding of the significant role that weevils play as pollinators,” de Medeiros concludes.

Source: Field Museum

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