Abstract
The eusocial termites are well accomplished in chemical communication, but how they achieve the communication using trace amount of no more than two pheromone components is mostly unknown. In this study, the foraging process and trail pheromones of the fungus-growing termite Odontotermes formosanus (Shiraki) were systematically studied and monitored in real-time using a combination of techniques, including video analysis, solid-phase microextraction, gas chromatography coupled with either mass spectrometry or an electroantennographic detector, and bioassays. The trail pheromone components in foraging workers were (3Z)-dodec-3-en-1-ol and (3Z,6Z)-dodeca-3,6-dien-1-ol secreted by their sternal glands. Interestingly, ratio of the two components changed according to the behaviors that the termites were displaying. This situation only occurs in termites whereas ratios of pheromone components are fixed and species-specific for other insect cuticular glands. Moreover, in bioassays, the active thresholds of the two components ranged from 1 fg/cm to 10 pg/cm according to the behavioral contexts or the pheromonal exposure of tested workers. The two components did not act in synergy. (3Z)-Dodec-3-en-1-ol induced orientation behavior of termites that explore their environment, whereas (3Z,6Z)-dodeca-3,6-dien-1-ol had both an orientation effect and a recruitment effect when food was discovered. The trail pheromone of O. formosanus was regulated both quantitatively by the increasing number of workers involved in the early phases of foraging process, and qualitatively by the change in ratio of the two pheromone components on sternal glandular cuticle in the food-collecting workers. In bioassays, the responses of workers to the pheromone were also affected by the variation in pheromone concentration and component ratio in the microenvironment. Thus, this termite could exchange more information with nestmates using the traces of the two trail pheromone components that can be easily regulated within a limited microenvironment formed by the tunnels or chambers.
Highlights
Pheromones are crucial for maintaining the cohesion of a termite colony
We investigated the chemical nature and the deposition and response regulation of the trail pheromone during the foraging of O. formosanus by using a combination of different techniques, including video analysis, solid-phase microextraction (SPME), gas chromatography (GC), gas chromatography coupled with mass spectrometry (GC-MS), GC coupled with electroantennographic detection (GC-EAD), and open-field trail-following bioassays
Regulation of Pheromone Deposition The nature of a termite recruitment trail pheromone has been the subject of much research
Summary
Pheromones are crucial for maintaining the cohesion of a termite colony. Information about trail direction or food quantity is given by trail pheromones [1] and sometimes by vibrations [2,3,4]. Differences between exploratory trails and recruitment trails, as well as the species-specific trail communication, have been observed many times in termites [5,6,7,8], despite the conservative chemical nature of the termite trail pheromones [9]. In bioassays, these differences could be both quantitative and/or qualitative [6,7,10]. In social behavior, the communication among individuals needs to be precise, resulting in both qualitative and quantitative regulation of trail pheromones. Multi-component trail pheromones were found in several termite species, as reviewed in reference [9], but how they express as much information using few pheromone components in only trace amounts is not known
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