The order Isoptera is traditionally split into seven families (Mastotermitidae, Termopsidae, Hodotermitidae, Kalotermitidae, Serritermitidae, Rhinotermitidae, Termitidae). All recent molecular studies (although producing contradictory results) agree on the paraphyletic nature of some traditional families. Above all it is the case of Rhinotermitidae, in which both, Serritermitidae and Termitidae probably form inner groups. The biology and life history is well-understood for principal genera of all of these families but Serritermitidae. The family Serritermitidae represents one of the most enigmatic taxa. Both its genera are Neotropical; Serritermes serrifer lives in outer walls of Cornitermes nests (Termitidae: Syntermitinae), while Glossotermes inhabits and feeds on decayed wood. We had recently many opportunities to collect Glossotermes oculatus, which is surprisingly abundant at certain places of the forest in French Guiana, especially around the Petit Saut dam.

Fig. 1 - Group of Glossotermes oculatus termites (soldiers and pseudergates) captured during collecting in the field.
Fig. 2 - Group of Glossotermes oculatus termites (soldiers, presoldier, pseudergates, neotenic reproductive, larvae) before fixation for electron microscopy.

First of all, we focused on its ontogeny to fill the gap in this field - Serritermitidae was the only family not studied from this aspect yet. Our results show that contrary to expectations, the working individuals of G. oculatus are in fact false workers (pseudergates), as they can moult into nymphs (wing-budded instar preceding the winged imago). The whole development starts from an egg, and through two larval, one or two pseudergate and a single nymphal instar leads to imago (with possible deviations toward soldier or neotenic reproductive). It means that there is no distinct true worker developmental line. On the other hand, the sex ratio is strongly male-biased in pseudergates and soldiers, which resembles derived situation in certain advanced taxa. Such developmental mode is exceptional in combination of primitive and derived features, and is unique among all termites.

We have also studied the defensive glands and behaviour of G. oculatus soldiers. Three glands are presumably involved in defense: labral, frontal, and labial glands. Labral gland is located at the ventral side of labrum, and its secretion impregnates the mandibular edges and gets into the body of the opponent by mandibular bite. It is formed by both, class 1 and 3 secretory cells.

Labial glands are located about thoraco-abdominal boundary, and produce water-carried secretion released from mouth during the bite.

Fig. 3 - TEM picture of labral gland in a soldier of Glossotermes oculatus. Fig. 4 - TEM picture of a part of labial gland acinus in a soldier of Glossotermes oculatus. Note the large amount of connective tissue in between secretory cells.

Frontal gland in G. oculatus soldiers is present as a huge, blind-end sac stretched between posterior head and mid abdomen. It is filled with bright yellow secretion, which is released by a rupture of the body wall (autothysis) at the dorsal side of cervix.

Fig. 5 - TEM picture of frontal gland epithelium in a soldier of Glossotermes oculatus              Note the lack of cuticular intima (usually separating secretory cells from their products).

When colony of G. oculatus is under attack, termites (except soldiers) are retreating deeper in the system of galleries. Soldiers are first trying to stop attacker by mandibular bites, but after certain time sacrifice themselves by frontal gland autothysis. The frontal gland secretion stiffens at the air, and the soldier remains stuck to the wall of a gallery, but living for quite a long time, what represents an efficient way of blocking the gallery against intruders.

References

1. Bourguignon T., �obotn�k J., Hanus R. & Roisin Y.:
   Developmental pathways of Glossotermes oculatus (Isoptera, Serritermitidae): at the cross-roads of worker caste evolution in termites.
   Evolution & Development 11: 659-668, 2009
    
2. �obotn�k J., Bourguignon T., Hanus R., Weyda F. & Roisin Y.:
   Structure and function of defensive glands in soldiers of Glossotermes oculatus (Isoptera: Serritermitidae).
   Biological Journal of the Linnean Society 99: 839-848, 2010.

Research team

Jan �obotn�k, Thomas Bourguignon, Yves Roisin, Rober Hanus, Frantisek Weyda

Related themes on our web pages

Termites (part I)
Termites (part II)