Ant larvae control parental care by using odor signals

Adults and larvae of the clonal raider ant Ooceraea biroi.
Photo Credit: © Anna Schroll

Scientific Frontline: Extended "At a Glance" Summary: Chemical Control of Parental Care by Ant Larvae

The Core Concept: Larvae of the clonal raider ant (Ooceraea biroi) release a specific volatile brood pheromone that temporarily suppresses egg-laying in adult ants to prioritize parental care.

Key Distinction/Mechanism: Rather than relying on physical contact to secure care, larvae actively govern adult behavior through chemical communication. By emitting the compound methyl-3-ethyl-2-hydroxy-4-methylpentanoate (MEHMP), larvae pause adult reproduction, keeping the entire colony synchronized between brood care and egg-laying phases. Exposure to synthetic MEHMP is sufficient to inhibit adult reproduction without any larvae present.

Major Frameworks/Components: 

• Parthenogenetic Reproduction Cycle: In the absence of queens, all Ooceraea biroi workers reproduce asexually. To survive, the colony must strictly alternate between phases of egg-laying and brood care.
• MEHMP Pheromone Isolation: Researchers identified methyl-3-ethyl-2-hydroxy-4-methylpentanoate as the singular chemical compound emitted exclusively by the larvae to act as a reproductive inhibitor.
• Volatile Synchronization: Because MEHMP is an airborne chemical signal, it effectively synchronizes the reproductive cycle across the entire colony, including foraging workers who never make direct physical contact with the brood.

Branch of Science: Behavioral Biology, Chemical Ecology, and Entomology.

Future Application: These findings lay the groundwork for investigating how odor perception directly controls the hormonal regulation of reproduction in insect brains. Furthermore, understanding these chemical pathways could eventually inform the development of novel, biologically-based pest control strategies designed to disrupt the reproductive cycles of invasive ant species.

Why It Matters: As the first described brood pheromone in ants, this discovery fundamentally shifts the scientific paradigm regarding insect brood. It overturns long-held assumptions that ant larvae are merely passive recipients of care, revealing them instead as active architects capable of governing adult behavior and orchestrating complex colony dynamics.

Baptiste Piqueret and Yuko Ulrich with a colony of clonal raider ants in the laboratory.
Photo Credit: © Anna Schroll

A brood pheromone released by larvae of clonal raider ants temporarily suppresses egg-laying in adult ants 

The Lise Meitner Group Social Behavior, led by Yuko Ulrich, is conducting research on a special ant species: the clonal raider ant Ooceraea biroi. This ant species does not have queens. Instead, all workers are capable of reproducing asexually without mating, a process known as parthenogenesis. 

In most social insect species, however, the queens lay eggs while the workers care for the brood. These roles are clearly defined, with no alternation between egg-laying and brood care. In contrast, all females in Ooceraea biroi are capable of both reproduction and brood care, and the colonies alternate between these two phases. "We wanted to know which factors regulate the reproductive cycle — that is, the alternation between egg-laying and caring for offspring — in our ant system," explains lead author Baptiste Piqueret. 

Chemical communication instead of physical contact 

Previous studies have shown that the presence of larvae is crucial for regulating the egg-laying behavior of adult ants. However, it was unclear whether the larvae secured parental care through physical contact, behavior, or chemical signals. "Since ants have a highly developed sense of smell, we suspected that the larvae release a chemical signal that inhibits egg-laying," says Yuko Ulrich. 

These considerations motivated the research team to search for a specific chemical signal emitted by the larvae. To accomplish this, the researchers collected volatile chemical compounds released during the ants' various developmental stages—from egg to larva to pupa to adult ant. They identified a compound emitted exclusively by the larvae, methyl-3-ethyl-2-hydroxy-4-methylpentanoate (MEHMP). "The biggest technical challenge was detecting this compound in extremely small quantities and synthesizing it in a way that allowed us to test it experimentally and ultimately confirm its role as a pheromone," says Yuko Ulrich. 

Brood pheromone in larvae controls parental fertility 

To eliminate the influence of physical contact, scientists designed an experimental setup that allowed ants to smell larvae without touching them. They also exposed the ants to synthetic MEHMP in behavioral experiments and compared the results with those of several control experiments to rule out other causes of the observed behavior. The results of these experiments clearly showed that the odor signal of the larvae was sufficient to suppress further egg-laying in adult ants, even when the odor was synthetic MEHMP and no larvae were present. 

"Ants go through various immature brood stages, including eggs and larvae. Due to the significant differences in their physiology, we initially assumed that we would find dozens of compounds in each brood stage and thus have several candidates for inhibiting fertility in adult ants. However, in our investigations, we found only one candidate,” Baptiste Piqueret summarizes the surprising result. 

Scientists also have an explanation for why ant larvae rely more on chemical messenger molecules than tactile signals. This is linked to the lifestyle of clonal raider ants. Although their reproductive phases alternate between caring for the brood and laying eggs, a division of labor still exists: some workers care for the larvae while others forage for food. Nevertheless, the reproductive cycle remains synchronized among all workers in the colony. Thus, the pheromone signal also reaches workers that do not come into contact with the larvae.  

Larvae as active members of ant societies 

MEHMP is the first described brood pheromone in ants. This challenges previous assumptions about the role of larvae in ant societies. "Larvae and brood in general have often been described as passive members of ant societies. However, this first ant brood pheromone suggests that larvae can play a much more active role in an ant society than was previously thought," says Baptiste Piqueret. In colonies of clonal raider ants, MEHMP helps synchronize brood care and reproduction. Since only the larvae produce this pheromone, the adults' fertility is no longer inhibited after pupation. The ants reproduce again by laying new eggs. As soon as the eggs develop into larvae, the ants stop laying eggs and return caring for the brood. 

Ant larvae release a pheromone that prevents their parents from reproducing again. This ensures that the parents devote themselves fully to their offspring's development before laying more eggs. 

The study raises new questions for Yuko Ulrich and her team. For instance, they want to determine how adult ants perceive the newly discovered pheromone, how the odor is processed in their brains, and how odor perception controls the hormonal regulation of reproduction. They also want to investigate whether similar pheromones exist in other ant species that are found exclusively in larvae. 

Published in journal: Proceedings of the National Academy of Sciences

Title: Offspring chemical control of adult reproductive transitions in a social insect

Authors: Baptiste Piqueret, Jerrit Weissflog, Sandra Tretter, Tim Zetzsche, Daniel Veit, Stefan Bartram, Rayko Halitschke, and Yuko Ulrich

Source/Credit: Max-Planck-Gesellschaft

Reference Number: bs040926_01

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