Christian Bordereau

Pheromones and Chemical Ecology of Dispersal and Foraging in Termites

Pheromones play a crucial role in the ecology of dispersal and foraging in termites. Sex-pairing pheromones possess a double role of long-range attraction to unite sexual partners and a short-range or contact attraction to maintain the pair during the tandem behaviour. Sex-pairing pheromones most often comprise a single compound capable of eliciting both behavioural effects. They appear very conservative in their evolution, and their role in the reproductive isolation of sympatric species greatly varies according to species. Species-specific sex-pairing pheromones consist of different major compounds or of a common major compound with species-specific minor components. Foraging is a collective behaviour mainly regulated by trail-following pheromones secreted from only one glandular source, the sternal gland. Trail-following pheromones may be also used by “one-piece” termites to colonise additional food sources. Although trail-following pheromones of termites have a double role of orientation and recruitment, they appear most often composed of only one compound. An alternative hypothesis is given to the postulated existence of a volatile ephemeral compound of recruitment and a long-lasting compound of orientation. Trail-following pheromones appear highly conserved in their chemical evolution (only 8 different pheromones for 60 species), even if a clear separation is observed between basal termites and more derived termites. The major ecological event of the external foraging was not related to a chemical evolutionary step of the trail-following pheromones. Pheromonal parsimony (the utilisation of a same molecule for multiple functions) is common in termites in the behavioural context of dispersal and foraging. The same molecule is used in many species as a sex-pairing pheromone and a trail-following pheromone, depending upon the pheromone concentration and the caste involved.

Ecdysone and ecdysterone in physogastric termite queens and eggs of Macrotermes bellicosus and Macrotermes subhyalinus

Abstract Physogastric queens and freshly laid eggs of two species of termites ( Macrotermes bellicosus and Macrotermes subhyalinus ) are found to contain high levels of ecdysteroids (molting hormones) as indicated by radioimmunoassay and Musca bioassay. Ecdysteroids are accumulated in the ovaries of the queen and then stored in the eggs since newly laid eggs contain ecdysteroid concentrations similar to those found in the ovaries. Gas chromatography-mass spectrometry demonstrates that ecdysone (α-ecdysone) as well as ecdysterone (β-ecdysone) are present in queen ovaries and in eggs and that ecdysone is quantitatively the more important ecdysteroid in both ovary and eggs.

Vibratory Alarm Signals in Two Sympatric Higher Termite Species: Pseudacanthotermes spiniger and P. militaris (Termitidae, Macrotermitinae)

When they are disturbed, soldiers of the two termite species Pseudacanthotermes spiniger and P. militaris hit the substratum with their head, thereby producing sounds. High-speed video recordings allowed us to analyze the movement. The sound emissions were recorded and their temporal structure was analyzed. Artificial stimulation proved that head-banging acts as an alarm signal transmitted through the vibrations produced in the substratum. Perception of these vibrations induced a polyethic response. Workers reacted to head-banging by escaping. Minor soldiers reacted by escaping, becoming immobile, or head-banging, thereby indicating the existence of positive feedback in signal production. Differences in the time patterns of the drumming appeared between both species but could not be shown to play a role in species recognition.

Suicidal defensive behaviour by frontal gland dehiscence in Globitermes sulphureus Haviland soldiers (Isoptera)

Summary:Globitermes sulphureus is a well-known termite for the suicidal behaviour of the soldiers which liberate a sticky defensive secretion by rupturing their body. We have shown that this secretion is elaborated in a highly transformed frontal gland occupying a large part of the abdomen and the thorax, and not in the salivary glands as had been assumed until now. This special frontal gland without an outside opening is ruptured by violent contractions of the abdominal wall at the level of a weakness area of the sternal thoracic integument, just before the forecoxae. This soldier autothysis is efficient but represents only one of the components of the defensive strategy of the species which also uses a mechanical defense with mandibles and the intervention of an alarm pheromone recruiting congeners.

Isolation and identification of (3Z,6Z,8E)-3,6,8-Dodecatrien-1-ol in Reticulitermes santonensis Feytaud (Isoptera, Rhinotermitidae): Roles in worker trail-following and in alate sex-attraction behavior

Abstract (3Z,6Z,8E)-3,6,8-Dodecatrien-1-ol was isolated and identified by gas chromatography-mass spectrometry in workers and alates of Reticulitermes santonensis Feytaud (Isoptera, Rhinotermitidae). This unsaturated alcohol is about 10 times more abundant in alates than in workers. Synthetic (3Z,6Z,8E)-3,6,8-dodecatrien-1-ol is highly active in eliciting trail-following in workers, and the threshold concentration is about 0.1 pg/cm trail. In alates, it elicits trail-following in both sexes at low concentration and sex attraction in male alates at high concentrations. It is suggested that (3Z,6Z,8E)-3,6,8-dodecatrien-1-ol is the main component of the trail-following pheromone as well as the sex pheromone in Reticulitermes santonensis .

(Z)-dodec-3-en-1-ol, a novel termite trail pheromone identified after solid phase microextraction from Macrotermes annandalei.

(Z)-dodec-3-en-1-ol was isolated and identified by GC-MS as the major component of the trail-following pheromone from whole body and sternal gland extracts of workers of the fungus-growing termite, Macrotermes annandalei (Silvestri) (Termitidae, Macrotermitinae). For the first time, this trail pheromone was also identified by using solid phase microextraction from the surface of the secretory sternal gland of workers. Bioassays showed that synthetic dodecenol induced both orientation and recruitment behavioral effects. The activity threshold of (Z)-dodec-3-en-1-ol in eliciting trail-following is similar to that of (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol in the Rhinotermitidae, but amounts of dodecenol secreted are 100 times higher than those of dodecatrienol. There is about 1 ng of (Z)-dodec-3-en-1-ol per worker. Artificial trails made of synthetic dodecenol are able to compete with natural trails in the field. The activity duration of synthetic (Z)-dodec-3-en-1-ol trails is shorter than that of trails made from whole sternal secretion of workers. Observations showed that (Z)-dodec-3-en-1-ol is probably the only major component of the trail-following pheromone of M. annandalei and that it could be associated with other compounds in a pheromonal blend providing specificity and/or stability to trails.

Burial behaviour by dealates of the termite Pseudacanthotermes spiniger (Termitidae, Macrotermitinae) induced by chemical signals from termite corpses

In order to maintain healthy colonies, termite workers dispose of the cadavers of dead nest mates by cannibalism, burial, or necrophoresis. However, when multiple reproductives found a new colony by pleometrosis, there are no worker castes at the early stages of the foundation to eliminate or isolate the corpses. In this study, we showed that in young pleometrotic colonies, reproductives of Pseudacanthotermes spiniger had the ability to perform this task. Because of the claustral conditions, and the potential inability of the dealates to feed on their own, their behaviour was restricted to the burial of the cadaver within the initial chamber. This burial behaviour, previously not reported in the reproductive caste of termites, appeared to be induced by chemical signals released by the corpses during decomposition, among which various fatty acids, indole and phenol were the most active. The burial finally resulted in the physical isolation of corpses, thus reducing the chances for opportunistic pathogens to spread among the rest of the individuals.

Sex pheromone identified after Solid Phase Microextraction from tergal glands of female alates in Cornitermes bequaerti (Isoptera, Nasutitermitinae)

Summary. For the first time, a termite sex pheromone secreted by tergal glands has been isolated and identified. In the mandibulate nasute termite Cornitermes bequaerti, pairing of swarming imagoes is mediated by a sex pheromone secreted by females from their tergal glands. These well developed sexual glands located in front of tergites 8, 9, 10 are essentially composed of class 1 and 2 cells, but also of some glandular units of class 3 cells. The major volatile compound of tergal secretion was isolated by solid phase microextraction (SPME) and identified by GC-MS as (3Z, 6Z, 8E)-dodecatrien-1-ol. Sex attraction bioassays with synthetic (3Z, 6Z, 8E)-dodecatrien-1-ol showed that this alcohol was the main component of the sex pheromone in C.bequaerti. The cellular origin and the key role of (3Z, 6Z, 8E)-dodecatrien-1-ol in the biology of termites are discussed.

Neocembrene A, a major component of the trail-following pheromone in the genus Prorhinotermes (Insecta, Isoptera, Rhinotermitidae)

Summary.The diterpene neocembrene A or (1E,5E,9E,12R)-1,5,9-trimethyl-12-(1-methylethenyl)-1,5,9-cyclotetradecatriene, known as the trail-following pheromone of the advanced Termitidae Nasutitermitinae Nasutitermes exitiosus and Trinervitermes bettonianus, has been identified after SPME-GC/MS as the major component of the trail-following pheromone of the Rhinotermitidae Prorhinotermitinae, Prorhinotermes canalifrons and P. simplex. In all the other Rhinotermitidae studied until now, the major component of their trail pheromones is dodecatrienol ((3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol). This biochemical data further add to the anatomical and molecular characteristics that give a special status to the taxon Prorhinotermes among Rhinotermitidae. In Prorhinotermes canalifrons and P. simplex, neocembrene A was the only secretory compound specific to the sternal gland surface that could be detected after SPME. It elicited orientation as well as recruitment behavioral effects. However, the comparison of the respective biological activities triggered by neocembrene A and by sternal gland secretion suggests that minor components of the latter are acting in synergy with neocembrene A.

Species specificity of trail pheromones of fungus-growing termites from northern Vietnam

Summary: Trail-following pheromones were studied in four fungus-growing termites from northern Vietnam: Macrotermes annandalei, M. barneyi, Odontotermes hainanensis and O. maesodensis. From bioassays, we suggest that trail pheromones of these species are composed of a common or anony-mous signal, as well as species-specific signals. The anonymous signal has been identified by GC-MS as (Z)-dodec-3-en-1-ol for each species from extracts of sternal glands and from solid phase microextraction of the surface of their sternal gland. This compound is secreted in much higher quantities (up to 1.4 ng/worker) than dodecatrienol, another anonymous signal of trail-following in termites. (Z)-dodec-3-en-1-ol is an anonymous signal of trail-following for numerous fungusgrowing termites, including African termites M. bellicosus and M. subhyalinus, but is not ubiquitous for all Macrotermitinae. Trail specificity is much more pronounced between species of different genera than between congeners. Species-specific compounds were not identified.