Photo: Laura Chavarría-Pizarro
Published on 07/08/2024
By André Julião | Agência FAPESP – Studying the natural history of wasps is risky. They are notoriously aggressive and have a painful sting, and researchers may suddenly find that the wasp colony being studied has abandoned a nest to settle somewhere unknown, making further data collection impossible.
According to an innovative study by a group of Brazilian scientists, these are successful survival strategies used by paper wasps known as Epiponini, a tribe of Neotropical eusocial wasps, enabling the several dozen species concerned to evolve and flourish for the last 55 million years. Their societies are highly complex in terms of nest construction, foraging methods and, above all, social interactions.
In the 1970s, research showed that an ancient dominance hierarchy strategy whereby a single queen is responsible for reproduction and aggressively prevents other females in the same colony from laying eggs had been replaced by coexistence of queens that do not compete for reproduction but are expelled by workers if they fail to exhibit certain kinds of behavior.
Through darts (sudden attacking moves), ritual displays and even bites, workers submit queens to their control, and only the fittest of them are able to reproduce, assuring the survival of the colony.
In the new study, the researchers succeeded in confirming that this reproductive strategy occurs in all species of the Epiponini tribe, only a few of which had been studied previously. However, they also found that the behaviors used by workers to test queens are not identical in all species but have evolved in some groups to become less violent and more stereotyped.
The findings are described in an article published in the journal Cladistics. The authors are affiliated with São Paulo State University (UNESP) and the University of São Paulo (USP).
“We found that in the most recent branches of their phylogeny [or evolutionary tree], workers and queens began to develop more complex and stereotyped behaviors instead of biting and attacking. Furthermore, queens have developed a larger repertory of behaviors to signal their potential and avoid being expelled from the colony,” said Fernando Noll, a professor at UNESP’s Institute of Biosciences, Letters and Exact Sciences (IBILCE) in São José do Rio Preto and last author of the article.
The study was part of two projects supported by FAPESP: “Countering the taxonomic impediment of aculeate wasps: micro- and macroregional visions of Neotropical fauna” and “Molecular phylogeny of Epiponini and the relationships among basal genera (Hymenoptera, Vespidae)”. The former is being conducted under the aegis of the FAPESP Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP).
In previously published work, the group described the most complete phylogeny of Epiponini to date, laying a foundation for the latest results. Besides the existence of more than one queen, another trait that distinguishes paper wasps from other wasps and from bees is the fact that workers control egg production by these fertile females (read more at: agencia.fapesp.br/35677).
Brazil and Costa Rica
Observing how these paper wasps behave in their nests was the research interest of Laura Chavarría-Pizarro, then a PhD candidate at the University of São Paulo’s Ribeirão Preto School of Philosophy, Sciences and Letters (FFCLRP) with a scholarship from FAPESP.
An opening had to be made in the nest’s protective envelope in order to observe the interior. At times, a piece of red plastic was used to cover up the hole, since these wasps cannot see the color red and could still be observed through the material.
“Taking into account all the tests I performed, not to mention opening the nests and marking individuals [to distinguish queens from workers], they didn’t sting me very much. Of course, I was wearing protective clothing,” said Chavarría-Pizarro, now a professor at the Costa Rican Technological Institute’s School of Biology in Cartago.
Part of the fieldwork was conducted in Costa Rica, her native country, where she was able to observe nests of six out of the nine species studied (all except three of which belong to the Epiponini tribe).
The study involved an analysis of 15 colonies – six in Brazil and nine in Costa Rica. The researchers documented 51 behaviors, detailing action and response, and noting whether a queen or worker was involved in each case. The wasps were observed directly or in previously recorded videos.
Dancing workers
One of the most important behaviors demonstrating a queen’s reproductive potential is known as a “bending display”, in which the queen bends her abdomen toward the worker. This is typically a response to a “dance” involving shaking of the entire body by the worker. If the queen does not respond, she is forced out of the colony.
According to the article, the study showed that the bending display has been in use for 55 million years, although a variation (called bending display 2) dates from some 30 million years ago. In the species that emerged most recently, both bending displays have to be performed to assure the queen’s survival.
“Curiously, the worker dance also dates from 30 million years ago, which suggests that this dance and bending display 2 are related,” Noll said.
In the older species, which do not do the worker dance, the tests used by workers to verify queen status are more aggressive, including darting and biting. These behaviors arose in the common ancestor of the Epiponini and are not shared by other polistine wasps. They were later replaced by the worker dance and other stereotyped behaviors.
In the same timeframe, queens began to exhibit a broader array of behaviors, probably because relationships were becoming more complex. “The behaviors are more refined and presumably offered advantages over all that violence,” Noll said.
“Paper wasps are very important, as they prey on other insects and help control species we humans consider pests. Understanding their behavior and survival strategies can help us coexist with them and assure their survival,” Chavarría-Pizarro concluded.
The article “Behavioral evolution of Neotropical social wasps (Vespidae: Polistinae): the queen selection process” is at: onlinelibrary.wiley.com/doi/abs/10.1111/cla.12529.
Source: https://agencia.fapesp.br/52162
