Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2011
Publication Date: 7/1/2011
Citation: Tarver, M.R., Schmelz, E.A., Scharf, M.E. 2011. Soldier caste influences on candidate primer pheromone levels and juvenile hormone-dependent caste differentiation in workers of the termite Reticulitermes flavipes. Journal of Insect Physiology. 57:771-777. Interpretive Summary: As social insects, termite colonies consist of distinct castes including soldiers, workers, and reproductives. The regulation of caste populations must be closely controlled to sustain the colony; likewise, agents that disrupt caste regulation could be used for pest control. Primer pheromones are chemical signals produced by certain castes that impact the developmental physiology of their nestmates, yet the details of these processes remain largely unknown. 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 worker termites only accumulate volatile terpenoids in the presence of soldiers which normally contain high levels. Assayed separately, the two primary terpenoids isolated from soldier heads displayed caste stimulatory and inhibitory activities in the modulation of developmental-hormone response thresholds leading to worker differentiation into presoldiers. An understanding of the chemical regulation of caste determination in termite colonies should enable the development of new tools for pest control.
Technical Abstract: Caste systems and the division of labor they make possible are common underlying features of all social insects. Multiple extrinsic factors have been shown to impact caste differentiation; for example, primer pheromones are chemical signaling molecules produced by certain castes that impact developmental physiology of nestmates. Thus, chemical signaling in social insect colonies is integral for maintaining caste homeostasis and a cohesive, efficient social structure. We examined the influences of terminally developed soldier termites (Reticulitermes flavipes) on (1) candidate primer pheromone levels and (2) caste differentiation in developmentally totipotent workers. Our findings provide evidence that the two main soldier terpenes, '-cadinene (CAD) and '-cadinenal (ALD), accumulate in nestmate workers only in the presence of soldiers, that soldiers can modulate developmental-hormone response thresholds of workers via CAD and ALD action, and that CAD and ALD (respectively) are caste stimulatory and inhibitory components of chemical blends present in soldier heads. Together these findings provided novel evidence that soldiers influence worker caste differentiation by either transferring terpene primer pheromonal compounds to workers, or by influencing de novo biosynthesis of these compounds in workers themselves.