Structure and function of defensive glands in soldiers of Glossotermes oculatus (Isoptera: Serritermitidae)

Abstract

The soldier caste represents the most conspicuous realization of termite eusociality, characterized by an extreme anatomical, behavioural, and physiological specialization. Numerous strategies have evolved in soldiers, including extreme adaptations such as self-sacrifice by autothysis. In the present study, we investigated the structure and function of defensive glands in Glossotermes oculatus soldiers aiming to understand their use in combat. Three glands are involved in defence: labral, frontal, and labial glands. Mandibles are used to bite the enemy, whereas the secretions of labral and labial glands are discharged into the wound. A striking characteristic of G. oculatus is the lack of the frontal pore; the secretion of the frontal gland is discharged by a rupture of the body wall. We hypothesized that this self-sacrifice is an efficient way of blocking a gallery under attack. A similar development of the frontal gland occurs in Serritermes serrifer, which supports the close relationship between the two genera inferred from morphological and genetic analyses.

A review on self-destructive defense behaviors in social insects

“…This process is comparable to the one described previously in carpenter ants, but in most species of termites the substance is secreted from the frontal gland rather than the mandibular gland (Sobotnik et al, 2010a). Ants that try to attack the termite are caught in the "sticky" substance, which congeals when exposed to air.…”

“…In the termite Globitermes sulphureus, the autothytic secretion is released through a rupture in the frontal gland and accumulates as a droplet at the inner face of the head capsule, but "very excited" workers contract violently and release the substance through the ventral side of thorax (Bordereau et al, 1997;Sobotnik et al, 2010a). This process is comparable to the one described previously in carpenter ants, but in most species of termites the substance is secreted from the frontal gland rather than the mandibular gland (Sobotnik et al, 2010a).…”

“…This type of defense has been observed in workers of the carpenter ant Camponotus saundersi and later in the Camponotus (Colobopsis) cylindricus complex (COCY) (Maschwitz and Maschwitz, 1974;Davidson et al, 2009Davidson et al, , 2011, but is particularly prominent in the soldier and worker castes of several termite species. To date, it has been reported in Glossotermes oculatus, Apilitermes longiceps, Globitermes sulphureus, the genera Dentispicotermes, and Ruptitermes (Sands, 1982;Bordereau et al, 1997;Sobotnik et al, 2010a;Deligne and De Coninck, 2006;Costa-Leonardo, 2004;Costa-Leonardo and Kitayama, 1991). While the morphological release structures and the chemical nature of these substances are variable, the application of this defensive behavior is very similar across disparate groups (Sobotnik et al, 2010a).…”

“…To date, it has been reported in Glossotermes oculatus, Apilitermes longiceps, Globitermes sulphureus, the genera Dentispicotermes, and Ruptitermes (Sands, 1982;Bordereau et al, 1997;Sobotnik et al, 2010a;Deligne and De Coninck, 2006;Costa-Leonardo, 2004;Costa-Leonardo and Kitayama, 1991). While the morphological release structures and the chemical nature of these substances are variable, the application of this defensive behavior is very similar across disparate groups (Sobotnik et al, 2010a). In all cases, the released substance is sticky and binds to predators, congealing when exposed to air and causing distress, immobility, or death to the target.…”

“…In Glossotermes oculatus, body rupture occurs from a frontal gland, and its main function appears also to be the blockage of galleries in the colony (Sobotnik et al, 2010a). When soldiers are disturbed outside the nest, they attempt to escape or hide rather than use autothysis, providing further evidence that autothysis in these termites is specialized for tunnel defense.…”