Sex-pairing pheromones and reproductive isolation in three sympatric Cornitermes species (Isoptera, Termitidae, Syntermitinae)

The Trail-Following Communication in Stylotermes faveolus and S. halumicus (Blattodea, Isoptera, Stylotermitidae)

Stylotermitidae appear peculiar among all termites, feeding in trunks of living trees in South Asia only. The difficulty to collect them limits the ability to study them, and they thus still belong to critically unknown groups in respect to their biology. We used a combination of microscopic observations, chemical analysis and behavioural tests, to determine the source and chemical nature of the trail-following pheromone of Stylotermes faveolus from India and S. halumicus from Taiwan. The sternal gland located at the 5th abdominal segment was the exclusive source of the trail-following pheromone in both S. faveolus and S. halumicus, and it is made up of class I, II and III secretory cells. Using gas chromatography coupled mass spectrometry, (3Z)-dodec-3-en-1-ol (DOE) was identified as the trail-following pheromone which elicits strong behavioural responses in workers at a threshold around 10- 4 ng/cm and 0.1 ng/gland. Our results confirm the switch from complex aldehyde trail-following pheromones occurring in the basal groups to simpler linear alcohols in the ancestor of Kalotermitidae and Neoisoptera.

A Review of Termite Pheromones: Multifaceted, Context-Dependent, and Rational Chemical Communications

Termite colonies, composed of large numbers of siblings, develop an important caste-based division of labor; individuals in these societies interact via intra- or intercaste chemical communications. For more than 50 years, termites have been known to use a variety of pheromones to perform tasks necessary for maintenance of their societies, similar to eusocial hymenopterans. Although trail-following pheromones have been chemically identified in various termites, other types of pheromones have not been elucidated chemically or functionally. In the past decade, however, chemical compositions and biological functions have been successfully identified for several types of termite pheromones; accordingly, the details of the underlying pheromone communications have been gradually revealed. In this review, we summarize both the functions of all termite pheromones identified so far and the chemical interactions among termites and other organisms. Subsequently, we argue how termites developed their sophisticated pheromone communication. We hypothesize that termites have diverted defensive and antimicrobial substances to pheromones associated in caste recognition and caste-specific roles. Furthermore, termites have repeatedly used a pre-existing pheromone or have added supplementary compounds to it in accordance with the social context, leading to multifunctionalization of pre-existing pheromones and emergence of new pheromones. These two mechanisms may enable termites to transmit various context-dependent information with a small number of chemicals, thus resulting in formation of coordinated, complex, and rational chemical communication systems.

Trail-Following Pheromones in the Termite Subfamily Syntermitinae (Blattodea, Termitoidae, Termitidae)

Trail-following behavior is a key to ecological success of termites, allowing them to orient themselves between the nesting and foraging sites. This behavior is controlled by specific trail-following pheromones produced by the abdominal sternal gland occurring in all termite species and developmental stages. Trail-following communication has been studied in a broad spectrum of species, but the "higher" termites (i.e. Termitidae) from the subfamily Syntermitinae remain surprisingly neglected. To fill this gap, we studied the trail-following pheromone in six genera and nine species of Syntermitinae. Our chemical and behavioral experiments showed that (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol is the single component of the pheromone of all the termite species studied, except for Silvestritermes euamignathus. This species produces both (3Z,6Z)-dodeca-3,6-dien-1-ol and neocembrene, but only (3Z,6Z)-dodeca-3,6-dien-1-ol elicits trail-following behavior. Our results indicate the importance of (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol, the most widespread communication compound in termites, but also the repeated switches to other common pheromones as exemplified by S. euamignathus.

Courtship Behavior Confusion in Two Subterranean Termite Species that Evolved in Allopatry (Blattodea, Rhinotermitidae, Coptotermes)

Congeneric species that live in sympatry may have evolved various mechanisms that maintain reproductive isolation among species. However, with the spread of invasive organisms owing to increased global human activity, some species that evolved in allopatry can now be found outside their native range and may have the opportunity to interact, in the absence of mechanisms for reproductive isolation. In South Florida, where the Asian subterranean termite, Coptotermes gestroi (Wamann), and the Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae) are invasive, the two species can engage in heterospecific mating behavior as their distribution range and their dispersal flight season both overlap. Termites rely on semiochemicals for many of their activities, including finding a mate after a dispersal flight. In this study, we showed that females of both species produce (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol (DTE) from their tergal glands as a shared sex pheromone. We suggest that both species primarily rely on an inundative dispersal flight strategy to find a mate, and that DTE is used as a short distance pheromone or contact pheromone to initiate and maintain the tandem between males and females. The preference of C. gestroi males for C. formosanus females during tandem resulted from the relatively high amount of DTE produced by tergal glands of C. formosanus females, when compared with those of C. gestroi females. This results in confusion of mating in the field during simultaneous dispersal flights, with a potential for hybridization. Such observations imply that no prezygotic barriers emerged while the two species evolved in allopatry for ~18 Ma.

Chemistry of the Secondary Metabolites of Termites

Isolation, structure determination, synthesis, and biochemistry of the low-molecular-weight compounds of the secretion of exocrine glands of termites are described, with an emphasis on pheromones and defensive compounds.

Sex-Pairing Pheromones in Three Sympatric Neotropical Termite Species (Termitidae: Syntermitinae)

Termite colonies are almost always founded by a pair of winged dispersers, in spite of the high costs and low success rates inherent in independent colony foundation. The dispersal flights of imagoes from natal colonies are followed by mate search, mediated by sex-pairing pheromones. Here, we studied the chemistry of sex-pairing pheromones and the related aspects of mate search in winged imagoes of two facultatively parthenogenetic species, Embiratermes neotenicus and Silvestritermes minutus, and an additional species from the same subfamily, Silvestritermes heyeri. All three species are widespread in the Neotropics, including the rainforests of French Guiana. After the dispersal flight and spontaneous loss of wings, females expose their hypertrophied tergal glands situated under abdominal tergites VIII - X. The females are attractive to males and, upon direct contact, the two sexes form characteristic tandems. Chemical analyses indicated that the females secrete species-specific combinations of unbranched, unsaturated C₁₂ primary alcohols from the tergal glands, (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol (approx. 200 pg per female) and (3Z)-dodec-3-enol (185 pg) in E. neotenicus, (3Z,6Z)-dodeca-3,6-dien-1-ol (3500 pg) in S. heyeri, and (3Z,6Z)-dodeca-3,6-dien-1-ol (300 pg) and (3Z)-dodec-3-enol (50 pg) in S. minutus. (3Z,6Z,8E)-Dodeca-3,6,8-trien-1-ol and (3Z,6Z)-dodeca-3,6-dien-1-ol act as major pheromone components in the respective species and mimic the function of female tergal gland extracts in electrophysiological and behavioral experiments. Biologically relevant amounts of the third compound, (3Z)-dodec-3-enol, elicited non-significant reactions in males of E. neotenicus and S. minutus, and slight synergistic effects in males of S. minutus when tested in combination with the major component.

Sex-pairing pheromone of Ancistrotermes dimorphus (Isoptera: Macrotermitinae)

Ancistrotermes dimorphus is a common Macrotermitinae representative, facultative inquiline by its life-style, occurring in South-East China. Sex pheromone is used for couple formation and maintenance, and it is produced by and released from the female sternal gland and is highly attractive to males. Based on our combined behavioral, chemical and electrophysiological analyses, we identified (3Z,6Z)-dodeca-3,6-dien-1-ol as the female sex pheromone of A. dimorphus as it evoked the tandem behavior at short distance, and the active quantities ranged from 0.01ng to 10ng. Interestingly, GC-MS analyses of SPME extracts showed another compound specific to the female sternal gland, (3Z)-dodec-3-en-1-ol, which showed a clear GC-EAD response. However, this compound has no behavioral function in natural concentrations (0.1ng), while higher amounts (1ng) inhibit the attraction achieved by (3Z,6Z)-dodeca-3,6-dien-1-ol. The function of (3Z)-dodec-3-en-1-ol is not fully understood, but might be linked to recognition from sympatric species using the same major compound, enhancing the long-distance attraction, or informing about presence of other colonies using the compound as a trail-following pheromone. The sternal gland secretion of Ancistrotermes females contains additional candidate compounds, namely (3E,6Z)-dodeca-3,6-dien-1-ol and (6Z)-dodec-6-en-1-ol, which are not perceived by males' antennae in biologically relevant amounts.

Sex-pairing pheromone in the Asian termite pest species Odontotermes formosanus

The sex-pairing pheromone of the black winged subterranean termite, Odontotermes formosanus (Shiraki) (Isoptera, Termitidae), was investigated using headspace-SPME, GC-MS, GC-EAD, and attraction bioassays. Females secrete the pheromone from their sternal gland to attract males. The sex-pairing pheromone is composed of (Z,Z)-dodeca-3,6-dien-1-ol and (Z)-dodec-3-en-1-ol, estimated at 9 to 16.64 ng and 0.2 to 0.54 ng, respectively. Both short- and long-distance sex attraction bioassays were employed to show that these compounds act in synergy at long distance, but only (Z,Z)-dodeca-3,6-dien-1-ol is active at short distance. The pheromone may be useful in efforts to control this pest, which is considered one of the most harmful termite species in Southeast Asia.