The eastern subterranean termite, Reticulitermes flavipes, is highly susceptible to desiccation and moisture is a critical factor for its survival. Termites possess a pair of salivary reservoirs (water sacs) that store water, which presumably are used to increase the humidity in unfavorable microclimates. The function and structure of salivary reservoirs in R. flavipes was investigated. This dissertation investigates the physiological mechanisms of water transport, specifically how water is maintained within the termite salivary reservoirs and how it is moved to new food sources.
The main objective of the first study was to measure the moisture change of a dry food source (cellulose pad) in the presence of R. flavipes workers during a 21-day period. Termites rapidly transported water to a dry food source, with the mean moisture content of the cellulose pad reaching ~7% just 3 hours after termites entered the test arena; the cellulose pad subsequently attained a maximum moisture content of ~46% at the 21-day observation. Salivary reservoir volume was smallest for termites removed from the food source in comparison to termites removed from the moist sand throughout the entire study (except on day 7). These data indicate that termites indeed use their salivary reservoirs as “water sacs” to relocate water from moist areas to dry resources.
The objective of the second study was to evaluate the variability of salivary reservoir dimensions among the various castes, when collected from different locations in laboratory colonies and at field sites. Salivary reservoirs dimensions differed among castes and stages when collected from food sources, shelter tubes and nurseries. Salivary reservoir volume was always larger for termites collected from food sources and nurseries. Salivary reservoirs were usually depleted in termites collected from shelter tubes. Soldiers always had the largest salivary reservoirs, followed by workers (which were categorized into three sizes based on head width). Alates and nymphs consistently had empty salivary reservoirs. These data demonstrate that salivary reservoir dimensions differ among stages and worker sizes; however this apparently is not related to any task specialization.
Current data are conflicting on how water enters the salivary reservoirs. This study investigated the route of water into the salivary reservoirs over a 6-hr period. When dehydrated workers were placed on moist sand, their crops were the first to fill (~80-85% full) after 15 minutes. Crops remained near full capacity (>75%) for 30–60 minutes before decreasing in size. An increase in salivary reservoir volume appeared to coincide with the decrease in crop volume. Salivary reservoir volumes were more than 50% full by 30-60 minutes and typically increased in size thereafter, though some colony variation was observed. Furthermore, water used in this study contained blue food coloring that was observed in the crop, but never in the salivary reservoirs. These data indicate that water reaches the salivary reservoirs via the hemolymph. Furthermore, preliminary gas chromatography and mass spectrometry results suggest the salivary reservoir contents may have a similar chemical profile to hemolymph. However, further analyses are required to determine if amino acids or sugars are present in the reservoirs.
An ultrastructural investigation was performed at the same time as the previous study to gather additional information on any mechanisms involved with water release and/or retention in the salivary reservoirs. Salivary reservoirs were composed of one layer of epithelial cells and were surrounded by an inner cuticle layer. Secretory-like cells were found in the reservoir walls and a lipid-like secretion was found in the reservoir lumen. No evidence of structures associated with an ionic gradient or valve-like structures where observed in the reservoirs. Two types of secretory cells were found in the salivary glands of workers. Type I secretory cells contained electron lucent secretion material, while Type II secretory cells contained electron dense secretion material. Furthermore, Type II could be separated into Type IIa and Type IIb, as Type IIa contained material of variable electron density and Type IIb was more uniform in density.
The salivary reservoirs are an important structure within the termite and the more information we gather on termite biology and colony dynamics, the better equipped we are to control them. Termite inspectors should not focus strictly on moisture-prone areas, as termites can relocate water to dry areas. This research also emphasizes the importance of educating homeowners on moisture reduction around homes. Furthermore, salivary reservoirs may be a candidate to target using RNA interference (RNAi)-based termiticides.