Termite exocrine systems: a review of current knowledge

In this review, we summarize the 22 exocrine glands hitherto described for termites (Isoptera), highlighting their distribution, morphological features, and likely function. The secretion from such glands displays a very important role in termite communication, but is also attributed to many other activities performed by these insects, including defense, building, and foraging, as well as physiological processes such as the synthesis of digestive enzymes, and antiseptic and lubricant compounds. Here, glands are divided into those associated with termite mouthparts and other head appendages, tegumentary glands with epithelial arrangement, those related to the reproductive apparatus, and glands which do not fit into these divisions. The exocrine systems in termites may be composed of classes 1, 2, and 3 secretory cells, which differ in how the glandular secretion is released. Moreover, they may exhibit a varied composition of secretory cell classes. Different glands may be involved in specific tasks and therefore produce specific compounds, although there are cases in which the same content is secreted by different glands, suggesting a functional plasticity. The chemical nature of these secretions and their role are well known for some glands, such as the frontal, salivary, tergal, and sternal ones. On the other hand, such aspects remain speculative or completely unknown for other glands. The number of termite exocrine glands is extremely low when compared to those described for eusocial Hymenoptera, and is a likely consequence of the higher diversity of species and chemical communication in the latter group. Moreover, vibroacoustic signals represent an important type of communication in termites. Further studies are encouraged to provide new insights into the occurrence and function of the exocrine systems in termites and how they modulate the different activities displayed by them.

Automated summary

In this review, the authors summarize the distribution, morphological features, and likely function of the 22 exocrine glands described for termites. These glands play a crucial role in termite communication and are also involved in defense, building, foraging, and physiological processes such as enzyme synthesis and the production of antiseptic and lubricant compounds. The exocrine systems in termites comprise different types of secretory cells and the composition of these cells varies among glands. Some glands have well-known chemical compositions and functions, while others remain speculative or unknown. The number of termite exocrine glands is relatively low compared to eusocial Hymenoptera species, possibly due to the higher species diversity and chemical communication in the latter. Further research is needed to understand the occurrence, function, and modulation of termite exocrine systems in different activities.