Involvement of the Salivary Glands in the Suicidal Defensive Behavior of Workers inNeocapritermes opacus(Blattaria, Isoptera, Termitidae)

Abstract

Suicidal behavior in termite workers is an extreme defensive strategy, probably a consequence of having a low number of soldiers available in the colony and there being high predation from enemies. We investigated the suicidal mechanism in workers of the Neotropical termite Neocapritermes opacus, which involves salivary gland autothysis followed by body cuticle rupture and the release of a defensive secretion. Autothysis was triggered by a physical stimulus such as a soldier bite that causes the protrusion of the salivary acini, burst reservoirs, and foregut. Histochemical and ultrastructural analyses showed salivary acini composed of peripheral parietal cells and two types of central cells, types I and II. Type I cells are filled with large electron-lucent secretory vesicles, which reacted positively to bromophenol blue and xylidine-Ponceau tests, indicating the occurrence of proteins. Type II cells are elongated and display smaller apical secretory vesicles. Parietal cells present an intracellular canaliculus with dense microvilli and cytoplasm rich in mitochondria and large electron-dense vesicles, which may participate in the self-destructive mechanism. Worker suicidal behavior was previously reported for N. taracua and N. braziliensis. N. opacus is a new species in which a salivary weapon has been developed and factors contributing to this altruistic response are discussed.

Salivary gland substances of the arboreal termite Nasutitermes corniger induce worker aggregation and gnawing of food substrate

“…The main function of termite salivary glands is to provide digestive enzymes that degrade cellulose, releasing smaller molecules that indicate resource quality (Saadeddin, 2014; Cypret & Judd, 2015; Talia & Arneodo, 2018). However, saliva is also used for nest building (Zachariah et al, 2017), defense against microorganisms (Matsuura et al, 2007) and enemies (Costa Leonardo et al, 2020), digestion of mutualistic bacteria, and parental recognition (Matsuura et al, 2007). In our study, we observed that substances from the salivary glands of last‐instar N. corniger workers acted as modulators of the foraging activity of workers on the food substrate.…”

Termite exocrine systems: a review of current knowledge

“…In workers, these glands also participate in activities such as trophallaxis, construction, and regulation of the nest microclimate (Grassé, 1982). In some species, workers provoke the rupture of the salivary glands (autothysis) as an extreme defensive behavior, releasing potentially harmful secretion on the enemies (Šobotník et al, 2012; Costa‐Leonardo et al, 2019, 2020). However, the defensive function of the salivary glands is more often attributed to soldiers, in which these structures are hypertrophied (Maschwitz & Tho, 1974; Howse, 1975; Wood et al, 1975; Šobotník et al, 2010a, b).…”

“…Such a defensive function is particularly well reported for the soldier caste and alate reproductives during swarming flights, occasions in which these individuals are vulnerable to massive predation (Lepage, 1991). Beyond their crucial role in nestmate interactions, exocrine glands in termites are involved in other physiological processes, including the production of digestive enzymes, synthesis of contents related to sperm storage and oviposition, and in extreme cases, self‐destructive behavior performed by suicidal individuals (Costa‐Leonardo, 1998a; Courrent et al, 2008; Ni & Tokuda, 2013; Costa‐Leonardo et al, 2019, 2020).…”