Pheromone communication is the cornerstone of eusocial insect societies since it mediates the social hierarchy, division of labor, and concerted activities of colony members. The current knowledge on molecular mechanisms of social insect pheromone detection by odorant receptors (ORs) is limited to bees and ants, while no OR was yet functionally characterized in termites, the oldest eusocial insect clade. Here, we present the first OR deorphanization in termites. We selected four OR sequences from the annotated antennal transcriptome of the termite Prorhinotermes simplex (Psammotermitidae), expressed them in Empty Neuron Drosophila, and functionally characterized them using single sensillum recording (SSR). For one of the selected ORs, PsimOR14, we obtained strong responses to the main component of P. simplex trail-following pheromone, the monocyclic diterpene neocembrene. PsimOR14 showed a narrow tuning to neocembrene with only one additional compound out of 67 tested generating non-negligible responses. We report on homology-based modeling and molecular dynamics simulations of ligand binding by PsimOR14. Subsequently, we used SSR in P. simplex workers and identified the olfactory sensillum responding to neocembrene, thus likely expressing PsimOR14. Finally, we demonstrate that PsimOR14 is significantly more expressed in worker antennae compared to soldiers, which correlates with higher sensitivity of workers to neocembrene.

• Keywords
• D. melanogaster, Prorhinotermes simplex, deorphanization, neuroscience, odorant receptor, pheromone receptor, termite, trail-following pheromone,
• MeSH
• Pheromones metabolism   MeSH
• Insect Proteins * metabolism   genetics   MeSH
• Isoptera * genetics   physiology   metabolism   MeSH
• Receptors, Odorant * metabolism   genetics   MeSH
• Receptors, Pheromone * metabolism   genetics   chemistry   MeSH
• Sensilla physiology   MeSH
• Arthropod Antennae metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Pheromones MeSH
• Insect Proteins * MeSH
• Receptors, Odorant * MeSH
• Receptors, Pheromone * MeSH

Effective defense is a common characteristic of insect societies. Indeed, the occurrence of specialized defenders, soldiers, has been the first step toward eusociality in several independent lineages, including termites. Among the multitude of defensive strategies used by termite soldiers, defense by chemicals plays a crucial role. It has evolved with complexity in advanced isopteran lineages, whose soldiers are equipped with a unique defensive organ, the frontal gland. Besides direct defense against predators, competitors, and pathogens, the chemicals emitted by soldiers from the frontal gland are used as signals of alarm. In this study, we investigated the chemical composition of the defensive secretion produced by soldiers of the termite Termitogeton planus (Isoptera: Rhinotermitidae), from West Papua, and the effects of this secretion on the behavior of termite groups. Detailed two-dimensional gas chromatography/mass spectrometry analyses of the soldier defensive secretion revealed the presence of four linear and nine monoterpene hydrocarbons. Soldier head extracts, as well as synthetic mixtures of the monoterpenes found in these extracts, elicited alarm behavior in both soldiers and pseudergates. Our results suggest that the alarm is not triggered by a single monoterpene from the defensive blend, but by a multi-component signal combining quantitatively major and minor compounds.

• MeSH
• Exocrine Glands chemistry   MeSH
• Pheromones chemistry   MeSH
• Isoptera chemistry   physiology   MeSH
• Monoterpenes chemistry   MeSH
• Gas Chromatography-Mass Spectrometry MeSH
• Social Behavior MeSH
• Hydrocarbons chemistry   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Pheromones MeSH
• Monoterpenes MeSH
• Hydrocarbons MeSH

A great diversity of defensive chemicals has been described in termite soldiers equipped with a unique defensive organ, the frontal gland. Along with the functional diversity of these compounds, reflecting the evolutionary history of particular lineages and their defensive strategies, a considerable degree of chemical variability often occurs among species and populations. Thus, the chemistry of termite defense may provide information on the phylogeny and geographic dispersal of species and populations. In this paper, we report on the anatomy of the frontal gland and on the diversity of soldier defensive chemicals in the sand termite, Psammotermes hybostoma, from nine colonies and five different localities in Egypt. Using gas chromatography-mass spectrometry, a total of 30 sesquiterpene hydrocarbons, or their oxygenated derivatives, were detected, and the chemical identity of most of them identified. In addition, a ketone, an ester, and a diterpene were identified in some colonies. Within colonies, the chemical composition was stable and did not differ among soldier size categories. However, there were pronounced quantitative and qualitative differences in frontal gland chemicals among colonies and geographic locations. The findings are discussed in a broader comparison with other termite taxa.

• MeSH
• Isoptera anatomy & histology   chemistry   MeSH
• Gas Chromatography-Mass Spectrometry MeSH
• Sesquiterpenes chemistry   isolation & purification   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Egypt MeSH
• Names of Substances
• Sesquiterpenes MeSH

The behavioral and electroantennographic responses of Prorhinotermes canalifrons to its soldier frontal gland secretion, and two separated major components of the secretion, (E)-1-nitropentadec-1-ene and (E,E)-alpha-farnesene, were studied in laboratory experiments. Behavioral experiments showed that both the frontal gland secretion and (E,E)-alpha-farnesene triggered alarm reactions in P. canalifrons, whereas (E)-1-nitropentadec-1-ene did not affect the behavior of termite groups. The alarm reactions were characterized by rapid walking of activated termites and efforts to alert and activate other members of the group. Behavioral responses to alarm pheromone differed between homogeneous and mixed groups, suggesting complex interactions. Antennae of both soldiers and pseudergates were sensitive to the frontal gland secretion and to (E,E)-alpha-farnesene, but soldiers showed stronger responses. The dose responses to (E,E)-alpha-farnesene were identical for both soldiers and pseudergates, suggesting that both castes use similar receptors to perceive (E,E)-alpha-farnesene. Our data confirm (E,E)-alpha-farnesene as an alarm pheromone of P. canalifrons.

• MeSH
• Pheromones physiology   MeSH
• Isoptera physiology   MeSH
• Sesquiterpenes metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• alpha-farnesene MeSH Browser
• Pheromones MeSH
• Sesquiterpenes MeSH