Researchers Find ‘Key Ingredient’ That Regulates Termite Caste System
A North Carolina State University entomologist has for the first time shown which specific chemicals are used by some termite queens to prevent other termites in the colony from becoming mommies like themselves.
In a study published online this week in Proceedings of the National Academy of Sciences, NC State’s Dr. Ed Vargo and colleagues from Japan and Switzerland show that a combination of two chemical compounds in a pheromone perfume emitted by egg-laying females known as secondary queens can inhibit other termites from developing into new queens. Moreover, the study shows that termite eggs also produce the caste-altering chemicals.
“This study opens up a whole new world into the mechanisms behind the ways colonies of termites and other social insects regulate themselves,” Vargo says. “With this long missing key ingredient now in hand, I expect we’ll see rapid progress in understanding how reproductive and nonreproductive termite castes develop.”
Secondary queens don’t prevent other termites in the colony from becoming mommies out of spite, Vargo says. It’s more a case of keeping the colony balanced with the correct numbers of caste members. Colonies need the proper proportion of workers who forage for food and take care of larvae, soldiers who defend the colony, and secondary queens who lay eggs to increase a colony’s numbers. The wrong balance could spell doom for the colony.
Termites molt frequently throughout their lives and can change castes depending on conditions in the colony. In the study, the scientists exposed different castes of termites that have the capacity to become secondary queens to both the actual pheromone perfume elicited from secondary queens and a synthetic version of the perfume. Both treatments prevented termites from becoming secondary queens.
Scientists have long believed that queen pheromones regulate caste development in social insects, but this finding is only the second such discovery in the past 50 years – when the term pheromone was coined by scientists. This is partly due, Vargo says, to scientists looking for the wrong types of chemicals.
“The pheromone – a combination of two chemicals called n-butyl-n-butyrate and 2-methyl-1-butanol – is a low-weight, volatile blend that acts directly on developing termites,” he says. That is in contrast to queen honey bees, for example, whose pheromone acts indirectly by regulating the queen-rearing behavior of worker bees.
NC State’s Department of Entomology is part of the university’s College of Agriculture and Life Sciences.
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“Identification of a pheromone regulating caste differentiation in termites”
Authors: Kenji Matasuura, Chihiro Himuro, Tomoyuki Yokoi and Yuuka Yamamoto, Okayama University; Edward L. Vargo, North Carolina State University; Laurent Keller, University of Lausanne
Published: The week of July 5, 2010, in Proceedings of the National Academy of Sciences
Abstract: The hallmark of social insects is their caste system: reproduction is primarily monopolized by queens, whereas workers specialize in the other tasks required for colony growth and survival. Pheromones produced by reining queens have long been believed to be the prime factor inhibiting the differentiation of new reproductive individuals. However, there has been very little progress in the chemical identification of such inhibitory pheromones. Here we report the identification of a volatile inhibitory pheromone produced by female neotenics (secondary queens) that acts directly on target individuals to suppress the differentiation of new female neotenics and identify n-butyl-n-butyrate and 2-methyl-1-butanol as the active components of the inhibitory pheromone. An artificial pheromone blend consisting of these two compounds had a strong inhibitory effect similar to live neotenics. Surprisingly, the same two volatiles are also emitted by eggs, playing a role both as an attractant to workers and an inhibitor of reproductive differentiation. This dual production of an inhibitory pheromone by female reproductives and eggs probably reflects the recruitment of an attractant pheromone as an inhibitory pheromone and may provide a mechanism ensuring honest signaling of reproductive status with a tight coupling between fertility and inhibitory power. Identification of a volatile pheromone regulating caste differentiation in a termite provides insights into the functioning of social insect colonies and opens important avenues for elucidating the developmental pathways leading to reproductive and nonreproductive castes.