Canopy beetles and flowering trees rely on each other in the Amazon, study

Held aloft by a canopy crane nearly 10 stories above the forest floor, Susan Kirmse observed and collected beetles in the rainforest canopy for an entire year. What did she find? Amazonian treetops are crawling with beetles, and they love little white flowers.

As part of her Ph.D. research for Leipzig University, Germany, Kirmse collected 859 species of beetles (6,698 individuals) from the canopies of 23 different tree species in a healthy lowland tropical rainforest in southern Venezuela in the late 1990s.

After decades of tedious work to identify all of the beetles and trees, Kirmse and her colleague, Caroline Chaboo from the University of Nebraska State Museum, have recently published a study in the Journal of Natural History. Kirmse and Chaboo suggest that flowering trees play an important role in maintaining canopy beetle diversity in the Amazon and that these trees are being visited by beetles more than any other insect order, including bees and butterflies.

More than 75% of the beetle species Kirmse collected were found living exclusively on flowering trees, and 36% were found only on trees with small white flowers. This, the authors say, means that flowering trees are important food and resource for canopy beetles.

A lot of research into pollination is dominated by the roles of bees and butterflies, Kirmse told Mongabay, but this work shows that, in a pristine rainforest, beetles have a huge role to play in maintaining the diversity of trees.

“Overall, this discovery shows that flowering trees are likely among the most important drivers for maintaining the high diversity of beetles in rainforests,” Chaboo wrote in The Conversation. “But this relationship goes both ways. Our study also suggests that beetles may be among the most underappreciated pollinators in tropical forests.”

Studying the canopy is logistically difficult. Canopy research methods must either bring a scientist into the canopy or bring the canopy down to the scientist. One famed entomologist, the late Terry Erwin, chose the latter. He famously pointed a fog machine up into tropical trees, killing and catching the gassed bugs to reveal a cornucopia of arboreal insect diversity.

Kirmse used a slower, longer-term approach, going to the canopy to observe bugs both day and night and across seasons, giving us new insight into insect behavior. But much of the work happened on the ground, in labs and field museums. The authors worked closely with entomologists and botanists to identify the hundreds of beetles and tree species from the collections. This process took decades.

“There is a shortfall in expert taxonomists to even describe and identify the incredible diversity of the rainforest canopy let alone explore these species ecology,” Beulah Garner, the senior curator of the Carabidae Insects Division at the Natural History Museum, London, who was not involved in the study, told Mongabay.

“[T]his is a really valuable study providing observational data for other entomologists to work with and build upon as well as supporting the assertion that mass flowering trees are vitally important for the diversity and survival of canopy dwelling beetles,” Garner added.

Political instability in Venezuela has put the Surumoni Crane Project, a cooperation between the Austrian Academy of Science and the Venezuelan government, out of commission, so researchers have been unable to return to this particular forest. But Kirmse’s year in the canopy yielded several publications on the taxonomy, behavior, and ecological roles of beetles in tropical forests, as well as the relationships between canopy beetles and trees.

Among these findings are that scarab beetles (Scarabaeidae family) track food resources in the canopy, depleting one tree before they move to the next. Kirmse and colleagues found that 55 beetle species relied exclusively on the nectar found in extrafloral nectaries (special nectar pockets on flowers) for their food, and that some beetles, such as click beetles, were nocturnal, only coming out to the flowers at night.

During her time in the trees, in the late 1990s, Kirmse was also one of the few women in the field of canopy science. Garner, who has also conducted research in the canopy, shared a similar experience.

“Mostly in my fieldwork I’ve been the only female in a team,” Garner said. “There is no reason that more women shouldn’t be included in this field, and in particular women native to the countries where this exploration is taking place. This is really important, that biologists, entomologists gain this training from the current experts, so they can one day lead teams and research in-country.”

The need for this research is becoming dire. Worldwide, insect populations are plummeting in what has been called “the great insect dying.” To fight this decline, Chaboo says, “researchers and conservationists must understand the ecological connections between insects and their food plants.” Long-term studies, she says, can “help unravel the complexity of diversity.”

“[I]t is clear that researchers must work together to understand the mysteries of life on Earth,” Chaboo said. “[B]iologists are racing the clock.”

To learn more about insect declines, see Mongabay’s investigative series “The Great Insect Dying.”

Banner image of  scarab beetles on little white flowers in the canopy by Susan Kirmse (CC BY-ND). 

Citation:

Kirmse, S., & Chaboo, C. S. (2020). Flowers are essential to maintain high beetle diversity (Coleoptera) in a Neotropical rainforest canopy. Journal of Natural History, 54(25-26), 1661-1696. doi:10.1080/00222933.2020.1811414

Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough_

FEEDBACK: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.