ARS | Publication request: Effects of soldier-derived terpenes on soldier caste differentiation in the termite Reticulitermes flavipes

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 2009
Publication Date: February 6, 2009
Citation: Tarver, M.R., Schmelz, E.A., Rocca, J.R., Scharf, M.E. 2009. Effects of soldier-derived terpenes on soldier caste differentiation in the termite Reticulitermes flavipes. Journal of Chemical Ecology. 35: 256-264.

Interpretive Summary: As social insects, termites colonies consist of castes consisting of soldiers, workers, and reproductives. The regulation of resource distribution between these castes must be closely controlled to sustain the colony; likewise, agents that disrupt caste regulation are sought after as a means to control these pests. While termites are believed to utilize specific biochemicals to maintain caste regulation within the colony, the specific mechanisms are not precisely known. In collaboration with researchers at the University of Florida, scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that volatile terpenoids present in the extracts of soldier termite heads serve as primer pheromones by significantly enhancing soldier caste formation from workers in the presence of insect juvenile hormone. This effect was not entirely specific as related sesquiterpene volatiles exhibited similar primer pheromone-like activities. These findings reveal a novel primer pheromone-like function for soldier-derived terpenes in termites, and demonstrate that volatile terpenoids synergize juvenile hormone dependent soldier caste differentiation. An understanding of the chemical regulation of caste determination in termite colonies will enable the development of new tools for pest control.

Technical Abstract: Primer pheromones play key roles in regulating division of labor, which is one of the most fundamental and defining aspects of insect sociality. Primer pheromones are chemical messengers that transmit hormone-like messages among colony members; in recipients these messages can either induce or suppress phenotypic caste differentiation. Here, we investigated soldier-caste-derived chemicals as possible primer pheromones in the lower termite Reticulitermes flavipes, a species for which no primer pheromones have yet been identified. We determined that soldier head extracts (SHE), when provided to totipotent workers along with the insect morphogenetic juvenile hormone (JH), significantly enhanced soldier caste differentiation. When applied alone, however, SHE had no impacts on caste differentiation, survivorship, or any other aspect of worker biology. These findings support that soldier-derived chemicals serve as primer pheromones that enhance the action of the endogenous morphogenetic hormone JH. The SHE chemicals have no discernable impacts on caste differentiation when applied by themselves, and thus, apparently when received under natural conditions by non-receptive individuals with presumably low JH titers. Gas chromatography-mass spectrometry analysis putatively identified two analogs of the terpene cadinene as the most plentiful components of R. flavipes SHE. Validative bioassays with commercially available cadinene confirmed its activity. However, several other previously identified terpenes were also significantly active. These findings reveal a novel primer pheromone-like function for soldier-derived terpenes in termites, and further suggest convergent evolution of terpene functions in enhancing JH-dependent soldier caste differentiation.