Formosan Subterranean Termite (Isoptera: Rhinotermitidae) Soldiers Regulate Juvenile Hormone Levels and Caste Differentiation in Workers

Abstract

A caste structure is maintained in termite societies and juvenile hormone (JH) is generally regarded as the most important regulator in these termite colonies. Here, we demonstrate that the soldier caste regulates JH in workers of Coptotermes formosanus Shiraki. Worker termites (80 Ð100 individuals) were placed in petri dishes with 0, 5, 10, or 20% soldiers. JH III titers of groups of these workers were monitored at 14, 28, 42, and 56 d. Any changes in soldier caste proportions also were noted at each sample date. On the Þrst sample date, the JH levels in workers were similar among treatments with different initial soldier proportions, and no new soldiers were formed. Over the next three sample dates, the worker JH levels were higher for low initial soldier proportion treatments and vice versa. Concurrently, soldier formation increased with lower initial soldier proportions. JH titers in workers showed a positive and statistically signiÞcant relationship to soldier numbers until a certain soldier proportion was reached. These results provide evidence that soldier caste proportions regulate JH levels and thereby caste differentiation in workers. The means by which this regulatory mechanism may proceed is discussed.

Social exploitation of hexamerin: RNAi reveals a major caste-regulatory factor in termites

“…Workers have three developmental potentials: (i) status quo molts in which they remain as workers, (ii) differentiation into the single-instar presoldier stage (followed immediately by molting into the soldier caste), or (iii) differentiation into apterous and eyeless third-form reproductives that assume identical functions as second-form reproductives. JH plays a key role in presoldier differentiation and worker caste maintenance (9,12). At high titers, JH induces presoldier differentiation from workers, whereas at lower titers status quo worker-to-worker molts take place.…”

“…From the perspective of cellulase expression alone (5, 6) (X.Z., unpublished data), maximizing worker numbers would clearly enhance colony nutritional status, and thus overall colony fitness. Moreover, if soldier caste members are truly capable of regulating reproductive differentiation (12,15), the hexamerin mechanism would take on even broader importance for maintaining status quo colony conditions. It has been hypothesized that caste differentiation in paper wasps evolved through exploitation of a developmental diapause switch (27), and that the foraging division of labor in the honey bee has evolved through co-option of a reproductive genetic network that includes the vitellogenin protein (28).…”

“…The morphogenesis of workers to presoldier and soldier caste phenotypes is induced by two-to fivefold increases in titers of the insect morphogenetic hormone, juvenile hormone (JH) III (9,12). Therefore, socioregulatory factors would be expected to exist that maintain a status quo workforce via modulation of JH production [e.g., JH-suppressive allatostatins (13)], or that in some way buffer JH action downstream of its synthesis.…”

“…Workers also retain the ability to differentiate to soldier caste members that are incapable of feeding and reproduction. Additionally, although the precise mechanism remains unknown, termite soldiers are capable of down-regulating the JH titers of nestmates (9,12), possibly facilitating reproductive differentiation (12); thus, as postulated by Henderson (15), the soldier caste apparently does serve broader roles beyond defense alone. This plasticity suggests a unique need by termites for specialized physiological adaptations that suppress worker differentiation to other caste phenotypes.…”

Effects of Soldier-Derived Terpenes on Soldier Caste Differentiation in the Termite Reticulitermes flavipes

“…Individuals in termite colonies with the same genetic background can differentiate into alternate phenotypes depending on a number of intrinsic and extrinsic factors (Lenz, 1976;Greenberg and Tobe, 1984;Koshikawa et al, 2005;Scharf et al, 2007). One intrinsic factor is juvenile hormone (JH) (Scharf et al, 2003b;Raina, 2004, 2005;Mao et al, 2005). Juvenile hormone is a morphogenetic hormone produced by a neurosecretory gland (the corpus allatum) that has a broad range of developmental and physiological effects (Wigglesworth, 1935;Schal et al, 1997;Truman and Riddiford, 1999;Gilbert et al, 2000;Truman et al, 2006).…”