Identification of a queen and king recognition pheromone in the subterranean termite Reticulitermes flavipes

Biostimulatory effects of boar seminal gel, saliva and semen on sexual behavior of young boars, gilts and sows

The present study aimed to identify novel biostimulatory compounds in boar seminal gel (SG), saliva and semen using Gas chromatography-mass spectrometry (GC-MS). The bio-stimulatory effect of SG, SG + saliva and SG + semen on young boar for semen collection as well were employed to study bio-stimulatory effects on gilts and sows. Distilled water (DW) exposure was kept as control. SG, saliva and semen were screened for total 105, 96 and 89 compounds. The highest concentration was of alkanes followed by sugar alcohols, then hydrocarbons, amino acids and fatty acids. Elaidic acid was the novel compound identified in pigs. Significantly higher (p < 0.05) number of males got trained in exposure to SG (80%), SG + saliva (75%) and SG + semen (75%) than control (0%). The time (hrs) taken by young boars to get trained on exposure to combination of SG + saliva (244 ± 22.19) and SG + semen (216 ± 13.14) was lesser (p < 0.05) than SG (356 ± 61.85) alone. Interval (hrs) from initiation of exposure for exhibition of different sexual behaviour by males on exposure to SG, saliva and semen was lesser (p < 0.05) than control. Significantly (p < 0.05) higher number of females showed estrus response to exposure of SG (72.72%), SG + saliva (69.23%) and SG + semen (76.92%) than control (0). Interval (hrs) taken to exhibit estrus was shorter (p < 0.05) in females exposed to SG + saliva (201.88 ± 12.66), SG + semen (198.20 ± 9.42) than SG (262.14 ± 20.06) alone. Interval (hrs) for exhibition of different sexual behaviour by females on exposure to SG + saliva and SG + semen was lesser (p < 0.05) than control. In conclusion, novel compounds were identified in boar seminal gel, saliva and semen with biostimulatory properties have been identified in boar SG, saliva and semen. The combined exposure of SG with saliva and semen has more intense biostimulation effect than SG alone for training of young boars and estrus induction in gilts and sows. Such compounds biostimulatory effects can be exploited for augmenting reproductive efficiency in pigs.

Step-induced double-row pattern of interfacial water on rutile TiO2(110) under electrochemical conditions

Metal oxides are promising (photo)electrocatalysts for sustainable energy technologies due to their good activity and abundant resources. Their applications such as photocatalytic water splitting predominantly involve aqueous interfaces under electrochemical conditions, but in situ probing oxide-water interfaces is proven to be extremely challenging. Here, we present an electrochemical scanning tunneling microscopy (EC-STM) study on the rutile TiO2(110)-water interface, and by tuning surface redox chemistry with careful potential control we are able to obtain high quality images of interfacial structures with atomic details. It is interesting to find that the interfacial water exhibits an unexpected double-row pattern that has never been observed. This finding is confirmed by performing a large scale simulation of a stepped interface model enabled by machine learning accelerated molecular dynamics (MLMD) with ab initio accuracy. Furthermore, we show that this pattern is induced by the steps present on the surface, which can propagate across the terraces through interfacial hydrogen bonds. Our work demonstrates that by combining EC-STM and MLMD we can obtain new atomic details of interfacial structures that are valuable to understand the activity of oxides under realistic conditions.

Termite primary queen - ancestral, but highly specialized eusocial phenotype

Termite eusociality is accompanied by flagrant caste polyphenism manifested by the presence of several sterile (workers and soldiers) and reproductive (imaginal and neotenic kings and queens) caste phenotypes. Imaginal kings and queens are developmentally equivalent to adults of other hemimetabolous insects but display multiple adaptations inherent to their role of eusocial colony founders, such as long lifespan and high fecundity. Herein, we summarize the recent advances in understanding the biology of imaginal (primary) queens as emblematic examples of termite polyphenism acquired during social evolution. We focus on the control of queen development, on dynamics in physiology and fecundity during the queen's life, on new findings about queen fertility signaling, and on proximate mechanisms underlying queen longevity.

Change of termite hindgut metabolome and bacteria after captivity indicates the hindgut microbiota provides nutritional factors to the host

The gut-dwelling microbiota is an indispensable part of termites. It is influenced by a series of factors, such as diet and captivity. The objectives of this study were to study the metabolic functions of hindgut microbiota and to investigate the influence of captivity on the hindgut microbiota. The dampwood termite Hodotermopsis sjostedti was reared in the laboratory for 6 months. We conducted the metabolome analysis of the fat body from the freshly-collected workers (FBF), the hindgut fluid of the freshly-collected workers (HFF), and the hindgut fluid of laboratory-maintained workers. In addition, the 16S rRNA genes from the hindgut bacteria in the freshly-collected and laboratory-maintained workers were sequenced. According to our results, the concentrations of metabolites associated with amino acid biosynthesis, vitamin biosynthesis, fatty acid biosynthesis, and cofactor biosynthesis were higher in HFF compared with those in FBF, suggesting that the hindgut microbiota provides nutritional factors to the host. However, after captivity, the concentrations of metabolites in the hindgut associated with amino acid biosynthesis, nucleotide sugar metabolism, vitamin biosynthesis, and carbon metabolism decreased, while those associated with the steroid hormone biosynthesis and ovarian steroidogenesis increased. Meanwhile, the 16S amplicon study revealed that the abundance of certain bacteria changed after captivity, such as uncultured Termite Group 1 bacterium, Candidatus Symbiothrix dinenymphae, and unclassified Desulfovibrio. Our findings show that captivity influences the hindgut microbiota and shed light on the metabolic potential of the hindgut microbiota.

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants, Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Nest-associated scent marks help bumblebees localizing their nest in visually ambiguous situations

Social insects such as ants and bees are excellent navigators. To manage their daily routines bumblebees, as an example, must learn multiple locations in their environment, like flower patches and their nest. While navigating from one location to another, they mainly rely on vision. Although the environment in which bumblebees live, be it a meadow or a garden, is visually stable overall, it may be prone to changes such as moving shadows or the displacement of an object in the scenery. Therefore, bees might not solely rely on visual cues, but use additional sources of information, forming a multimodal guidance system to ensure their return home to their nest. Here we show that the home-finding behavior of bumblebees, when confronted with a visually ambiguous scenario, is strongly influenced by natural scent marks they deposit at the inconspicuous nest hole when leaving their nest. Bumblebees search for a longer time and target their search with precision at potential nest locations that are visually familiar, if also marked with their natural scent. This finding sheds light on the crucial role of odor in helping bees find their way back to their inconspicuous nest.

Evidence of queen-rearing suppression by mature queens in the little fire ant, Wasmannia auropunctata

The little fire ant (LFA), Wasmannia auropunctata, is a serious invasive pest first reported on Hawaii Island in 1999, and has since spread and established itself across the island. LFA is considered one of the worst 100 invasive species and has significant ecological, agricultural, and public health impacts in invaded areas, which include much of the tropical New World. Although localized eradication efforts have proven successful, they are intensive and difficult to implement. Furthermore, LFA's high invasive-ability resists these control efforts in areas where the species is established and can re-infest treated areas. This research set out to determine whether LFA queens have a suppressant effect on new queen production in nests, as a first step in identifying a potential queen pheromone for LFA. A queen pheromone could offer a means to shutdown LFA reproductive capability, potentially by suppressing the production of new queens or inducing the execution of queens or queen-destined larvae. When queenless experimental nests and polygyne experimental nests were compared, six out of eight queenless nests successfully reared both new alate queens (2.25 queens/nest) and drones (3.63 drones/nest) to adulthood, whereas only three of eight polygyne nests reared sexual larvae that failed to develop to adulthood or even the pupal stage. These results suggest that dealate mature LFA queens suppress the production of new alate queens in LFA nests, and is the first evidence that LFA may utilize a queen pheromone.

Reproductives signature revealed by protein profiling and behavioral bioassays in termite

Proteins are known to be social interaction signals in many species in the animal kingdom. Common mediators in mammals and aquatic species, they have seldom been identified as such in insects' behaviors. Yet, they could represent an important component to support social signals in social insects, as the numerous physical contacts between individuals would tend to favor the use of contact compounds in their interactions. However, their role in social interactions is largely unexplored: are they rare or simply underestimated? In this preliminary study, we show that, in the termite Reticulitermes flavipes, polar extracts from reproductives trigger body-shaking of workers (a vibratory behavior involved in reproductives recognition) while extracts from workers do not. Molecular profiling of these cuticular extracts using MALDI-TOF mass spectrometry reveals higher protein diversity in reproductives than in workers and a sex-specific composition exclusive to reproductives. While the effects observed with extracts are not as strong as with live termites, these results open up the intriguing possibility that social signaling may not be limited to cuticular hydrocarbons or other non-polar, volatile chemicals as classically accepted. Our results suggest that polar compounds, in particular some of the Cuticular Protein Compounds (CPCs) shown here by MALDI to be specific to reproductives, could play a significant role in insect societies. While this study is preliminary and further comprehensive molecular characterization is needed to correlate the body-shaking triggering effects with a given set of polar compounds, this exploratory study opens new perspectives for understanding the role of polar compounds such as proteins in caste discrimination, fertility signaling, or interspecific insect communication.

Genome-Wide Analysis of the Odorant Receptor Gene Family in Solenopsis invicta, Ooceraea biroi, and Monomorium pharaonis (Hymenoptera: Formicidae)

Olfactory systems in eusocial insects play a vital role in the discrimination of various chemical cues. Odorant receptors (ORs) are critical for odorant detection, and this family has undergone extensive expansion in ants. In this study, we re-annotated the OR genes from the most destructive invasive ant species Solenopsis invicta and 2 other Formicidae species, Ooceraea biroi and Monomorium pharaonis, with the aim of systematically comparing and analyzing the evolution and the functions of the ORs in ant species, identifying 356, 298, and 306 potential functional ORs, respectively. The evolutionary analysis of these ORs showed that ants had undergone chromosomal rearrangements and that tandem duplication may be the main contributor to the expansion of the OR gene family in S. invicta. Our further analysis revealed that 9-exon ORs had biased chromosome localization patterns in all three ant species and that a 9-exon OR cluster (SinvOR4–8) in S. invicta was under strong positive selection (Ka/Ks = 1.32). Moreover, we identified 5 S. invicta OR genes, namely SinvOR89, SinvOR102, SinvOR352, SinvOR327, and SinvOR135, with high sequence similarity (>70%) to the orthologs in O. biroi and M. pharaonis. An RT-PCR analysis was used to verify the antennal expression levels of these ORs, which showed caste-specific expression. The subsequent analysis of the antennal expression profiles of the ORs of the S. invicta workers from the polygyne and monogyne social forms indicated that SinvOR35 and SinvOR252 were expressed at much higher levels in the monogyne workers than in the polygyne workers and that SinvOR21 was expressed at higher levels in polygyne workers. Our study has contributed to the identification and analysis of the OR gene family in ants and expanded the understanding of the evolution and functions of the ORs in Formicidae species.

Volatile Organic Compounds: A Promising Tool for Bed Bug Detection

The recent decades' resurgence of bed bugs as a public health concern in industrialized countries has driven an increased interest on new sustainable insecticide-free methods to monitor and control these ectoparasites. Current methods of detection rely mainly on visual inspection or canine scent detection, which are methods that are time-consuming, require experience, are non-specific or require costly mission repetitions. Volatile organic compounds (VOCs) are considered an environmentally friendly alternative and a promising approach for bed bug detection. An overview of the released literature on VOCs, their chemical characteristics and their role in bed bugs' intra- and inter-species communications allowed us to highlight the identification of 49 VOCs in Cimex lectularius (23 molecules) and C. hemipterus (26), which are emitted by both sexes during diverse compartments including aggregation (46), mating (11), defense (4), etc., and all life stages including exuviae or dead bed bugs as a principal indicator of infestation. The latter has a great importance for application of these semiochemicals in successful detection and control management of bed bugs and to prevent their further dispersion. This approach has the advantage of more reliability compared to conventional detection methods with no need for repeated inspections, household furniture moving or resident rehousing for bed bugs' VOC detection, which are commonly performed by active or passive sampling with absorbing tubes and analyzed by gas chromatography-based analytical platforms.

The effect of ergosterol on the allogrooming behavior of termites in response to the entomopathogenic fungus Metarhizium anisopliae

Termites have physiological and behavioral immunities that make them highly resistant to pathogen infections, which complicates biocontrol efforts. However, the stimuli that trigger the pathogen-avoidance behaviors of termites are still unclear. Our study shows that workers of Coptotermes formosanus exposed to the conidia of Metarhizium anisopliae exhibited a significantly higher frequency and longer duration of allogrooming behaviors compared with untreated termites. Volatile compounds in the cuticle of control termites and termites previously exposed to a suspension of M. anisopliae conidia were analyzed and compared using a gas chromatography-mass spectrometer (GC-MS). Our results showed that the amount of ergosterol differed between the fungus-exposed and control termites. Choice tests showed that termites significantly preferred to stay on filter paper treated with ergosterol (0.05, 0.1, or 1.0 mg/mL) compared with control filter paper. In addition, termites exposed to ergosterol followed by M. anisopliae conidia were allogroomed at a significantly higher frequency and for a longer duration than termites exposed to alcohol (the solvent used with the ergosterol in the ergosterol trials) alone followed by M. anisopliae conidia. These results showed that ergosterol may enhance the allogrooming behavior of termites in the presence of entomopathogenic fungi.

Identification of a queen primer pheromone in higher termites

It is long established that queens of social insects, including termites, maintain their reproductive dominance with queen primer pheromones (QPPs). Yet, the QPP chemistry has only been elucidated in a single species of lower termites. By contrast, the most diversified termite family Termitidae (higher termites), comprising over 70% of termite species, has so far resisted all attempts at QPP identification. Here, we show that the queen- and egg-specific sesquiterpene (3R,6E)-nerolidol acts as the QPP in the higher termite Embiratermes neotenicus. This species has a polygynous breeding system, in which the primary queen is replaced by multiple neotenic queens of parthenogenetic origin. We demonstrate that (3R,6E)-nerolidol suppresses the development of these parthenogenetic queens and thus mimics the presence of mature queen(s). It acts as an airborne signal and may be used to optimize the number of queens, thus being the key regulatory element in the special breeding system of E. neotenicus.

Room temperature bilayer water structures on a rutile TiO2(110) surface: hydrophobic or hydrophilic?

The lack of understanding of the molecular-scale water adsorbed on TiO2 surfaces under ambient conditions has become a major obstacle for solving the long-time scientific and applications issues, such as the photo-induced wetting phenomenon and designing novel advanced TiO2-based materials. Here, with the molecular dynamics simulation, we identified an ordered water bilayer structure with a two-dimensional hydrogen bonding network on a rutile TiO2(110) surface at ambient temperature, corroborated by vibrational sum-frequency generation spectroscopy. The reduced number of hydrogen bonds between the water bilayer and water droplet results in a notable water contact angle (25 ± 5°) of the pristine TiO2 surface. This surface hydrophobicity can be enhanced by the adsorption of the formate/acetate molecules, and diminishes with dissociated H2O molecules. Our new physical framework well explained the long-time controversy on the origin of the hydrophobicity/hydrophilicity of the TiO2 surface, thus help understanding the efficiency of TiO2 devices in producing electrical energy of solar cells and the photo-oxidation of organic pollutants.

Cuticular hydrocarbons as caste-linked cues in Neotropical swarm-founding wasps

Wasps (Vespidae) are important organisms to understand the evolution of social behaviour. Wasps show different levels of sociality, which includes solitary to highly eusocial organisms. In social insect species, queens and workers differ in physiology and morphology. The Neotropical swarm-founding wasps (Epiponini) show a variety of caste syndromes. In this clade, the caste-flexibility is a unique characteristic, in which workers can become queens and swarm to start a new nest. The investigation of the caste system comparing several Epiponini species show a clear-cut morphological distinction between queens and workers, with a morphological continuum between queens and workers. However, whether cuticular hydrocarbons (CHCs) are used as cues for caste recognition in swarm-founding wasps is still unknown. We studied whether CHCs may display caste-linked differences in eleven species of Epiponini wasps and if CHCs differences would follow morphological patterns. Our results suggest that queens and workers of Epiponini wasps are chemically different from each other at two levels, qualitatively and quantitatively, or merely quantitatively. This variation seems to exist regardless of their morphological traits and may be useful to help us understanding how chemical communication evolved differently in these species.

Molecular characterization and expression variation of the odorant receptor co-receptor in the Formosan subterranean termite

Subterranean termites live in underground colonies with a division of labor among castes (i.e., queens and kings, workers, and soldiers). The function of social colonies relies on sophisticated chemical communication. Olfaction, the sense of smell from food, pathogens, and colony members, plays an important role in their social life. Olfactory plasticity in insects can be induced by long- and short-term environmental perturbations, allowing adaptive responses to the chemical environment according to their physiological and behavioral state. However, there is a paucity of information on the molecular basis of olfaction in termites. In this study, we identified an ortholog encoding the odorant receptor co-receptor (Orco) in the Formosan subterranean termite, Coptotermes formosanus, and examined its expression variation across developmental stages and in response to social conditions. We found that C. formosanus Orco showed conserved sequence and structure compared with other insects. Spatial and temporal analyses showed that the Orco gene was primarily expressed in the antennae, and it was expressed in eggs and all postembryonic developmental stages. The antennal expression of Orco was upregulated in alates (winged reproductives) compared with workers and soldiers. Further, the expression of Orco decreased in workers after starvation for seven days, but it was not affected by the absence of soldiers or different group sizes. Our study reveals the molecular characteristics of Orco in a termite, and the results suggest a link between olfactory sensitivity and nutritional status. Further studies are warranted to better understand the role of Orco in olfactory plasticity and behavioral response.

Why does an obligate autogamous orchid produce insect attractants in nectar? - a case study on Epipactis albensis (Orchidaceae)

BACKGROUND

The flowers of some species of orchids produce nectar as a reward for pollination, the process of transferring pollen from flower to flower. Epipactis albensis is an obligatory autogamous species, does not require the presence of insects for pollination, nevertheless, it has not lost the ability to produce nectar, the chemical composition of which we examined by gas chromatography-mass spectrometry (GC-MS) method for identification of potential insect attractants.

RESULTS

During five years of field research, we did not observe any true pollinating insects visiting the flowers of this species, only accidental insects as ants and aphids. As a result of our studies, we find that this self-pollinating orchid produces in nectar inter alia aliphatic saturated and unsaturated aldehydes such as nonanal (pelargonal) and 2-pentenal as well as aromatic ones (i.e., syringaldehyde, hyacinthin). The nectar is low in alkenes, which may explain the absence of pollinating insects. Moreover, vanillin and eugenol derivatives, well-known as important scent compounds were also identified, but the list of chemical compounds is much poorer compared with a closely related species, insect-pollinating E. helleborine.

CONCLUSION

Autogamy is a reproductive mechanism employed by many flowering plants, including the orchid genus Epipactis, as an adaptation to growing in habitats where pollinating insects are rarely observed due to the lack of nectar-producing plants they feed on. The production of numerous chemical attractants by self-pollinated E. albensis confirms the evolutionary secondary process, i.e., transition from ancestral insect-pollinating species to obligatory autogamous.

A comprehensive review on the documented characteristics of four Reticulitermes termites (Rhinotermitidae, Blattodea) of China

Termites are known as social insects worldwide. Presently in China 473 species, 44 genera and 4 families of termites have been reported. Of them, 111 Reticulitermes species are widely spread in different zones of China. The dispersion flight season of these Chinese Reticulitermes species are usually started from February to June, but in some regions different species are distributed, sharing their boundaries and having overlapping flight seasons. These reasons become important sources of hybridization between two different heterospecific populations of termites. It was confirmed that the fertilized eggs and unfertilized eggs of some Reticulitermes termites have the capacity of cleavage. While the unfertilized eggs of R. aculabialis, R. chinensis and R. labralis cleaved normally and the only R. aculabialis unfertilized eggs develop in embryos. While, the R. flaviceps and R. chinensis were observed with their abnormal embryonic development, and not hatching of eggs parthenogenetically. They were reported more threatening to Chinese resources as they propagate with parthenogenesis, hybridization and sexual reproduction. Eggshell and macrophiles of eggs play important roles in species identification and control. Although, they are severe pests and cause a wide range of damages to wooden structures and products in homes, buildings, building materials, trees, crops, and forests in China's Mainland.

The cell invasion preference of Varroa destructor between the original and new honey bee hosts

Honey bees (Apis) are important pollinators for food crops and wild plants, but are facing great threats from pathogens and parasites, especially an obligate ectoparasitic mite, Varroa destructor. Cell invasion is a key step for V. destructor to reproduce, and the parasite displays remarkable host preference in this process. Varroa destructor made its host-shift from its original host, the Asian honey bee Apis cerana, to the new host, the European honey bee Apis mellifera several decades ago. However, it remains largely unstudied whether V. destructor shows a cell invasion preference between the two host species. Using cell invasion bioassays on a modified four-well arena, we showed that V. destructor significantly preferred to invade the worker and drone larvae of A. mellifera rather than A. cerana, suggesting that the new host is much more attractive to the parasite than the original one. Using gas chromatography-mass spectrometry (GC-MS), we revealed significant differences between the cuticular hydrocarbon (CHC) profiles of worker and drone larvae of the two bee hosts. The amounts of methyl-branched alkanes and alkenes (unsaturated CHCs), but not n-alkanes, were significantly different, and A. mellifera worker and drone larvae were found to express significantly higher amounts of methyl-alkanes, while A. cerana larvae produced higher amounts of alkenes. Cell invasion bioassays with glass dummies showed that the mites preferred the glass dummies coated with the CHCs of A. mellifera worker or drone larvae, which indicates a role of larval CHCs in mediating the preferential cell invasion of Varroa. The findings from this study extend our understanding of the host preference of V. destructor, and can potentially contribute to the development of effective strategies for mite control.

Comparative Antennal Morphometry and Sensilla Organization in the Reproductive and Non-Reproductive Castes of the Formosan Subterranean Termite

Antennae are the primary sensory organs in insects, where a variety of sensilla are distributed for the perception of the chemical environment. In eusocial insects, colony function is maintained by a division of labor between reproductive and non-reproductive castes, and chemosensation is essential for regulating their specialized social activities. Several social species in Hymenoptera display caste-specific characteristics in antennal morphology and diversity of sensilla, reflecting their differential tasks. In termites, however, little is known about how the division of labor is associated with chemosensory morphology among castes. Using light and scanning electron microscopy, we performed antennal morphometry and characterized the organization of sensilla in reproductive (female and male alates) and non-reproductive (worker and soldier) castes in the Formosan subterranean termite, Coptotermes formosanus Shiraki. Here, we show that the antennal sensilla in alates are twice as abundant as in workers and soldiers, along with the greater number of antennal segments and antennal length in alates. However, all castes exhibit the same types of antennal sensilla, including basiconicum, campaniformium, capitulum, chaeticum I, chaeticum II, chaeticum III, marginal, trichodeum I, and trichodeum I. The quantitative composition of sensilla diverges between reproductive and non-reproductive castes, but not between female and male alates or between worker and soldier castes. The sensilla display spatial-specific distribution, with basiconicum exclusively and capitulum predominantly found on the ventral side of antennae. In addition, the abundance of chemosensilla increases toward the distal end of antennae in each caste. This research provides morphological signatures of chemosensation and their implications for the division of labor, and suggests future neurophysiological and molecular studies to address the mechanisms of chemical communication in termites.

Effects of juvenile hormone in fertility and fertility-signaling in workers of the common wasp Vespula vulgaris

In the highly eusocial wasp, Vespula vulgaris, queens produce honest signals to alert their subordinate workers of their fertility status, and therefore they are reproductively suppressed and help in the colony. The honesty of the queen signals is likely maintained due to hormonal regulation, which affects fertility and fertility cue expression. Here, we tested if hormonal pleiotropy could support the hypothesis that juvenile hormone controls fertility and fertility signaling in workers. In addition, we aimed to check oocyte size as a proxy of fertility. To do that, we treated V. vulgaris workers with synthetic versions of juvenile hormone (JH) analogue and a JH inhibitor, methoprene and precocene, respectively. We dissected the treated females to check ovary activation and analyzed their chemical profile. Our results showed that juvenile hormone has an influence on the abundance of fertility linked compounds produced by workers, and it also showed to increase oocyte size in workers. Our results corroborate the hypothesis that juvenile hormone controls fertility and fertility signaling in workers, whereby workers are unable to reproduce without alerting other colony members of their fertility. This provides supports the hypothesis that hormonal pleiotropy contributes to keeping the queen fertility signals honest.

Vibratory behaviour produces different vibrations patterns in presence of reproductives in a subterranean termite species

Vibratory behaviours are widespread in social insects, but the produced vibrations remain poorly explored. Communication using vibrations is an efficient way to transmit information in subterranean environments where visual and odorant signals are less efficient. In termites, different vibratory behaviours are performed in different contexts like reproductive regulation and alarm signalling, but only few studies explored the structure of the produced vibrations (i.e., duration, number of pulses, amplitude). Here, we described several types of vibrations produced by a vibratory behaviour widespread in termites (body-shaking), which can be transmitted through the substrate and detected by other colony members. We analysed the structures of the emitted vibrations and the occurrence of the body-shaking events in presence/absence of reproductives and/or in presence/absence of a stress stimuli (flashlight) in the subterranean termite Reticulitermes flavipes. Interestingly, only the presence of the reproductives did influence the number of pulses and the duration of the emitted vibrations. Moreover, the first part of the emitted vibrations seems to be enough to encode reproductive information, but other parts might hold other type of information. Body-shaking occurrence did increase in presence of reproductives but only briefly under a flashlight. These results show that vibratory cues are complex in termites and their diversity might encode a plurality of social cues.

Genetic basis of chemical communication in eusocial insects

Social behavior is one of the most fascinating and complex behaviors in humans and animals. A fundamental process of social behavior is communication among individuals. It relies on the capability of the nervous system to sense, process, and interpret various signals (e.g., pheromones) and respond with appropriate decisions and actions. Eusocial insects, including ants, some bees, some wasps, and termites, display intriguing cooperative social behavior. Recent advances in genetic and genomic studies have revealed key genes that are involved in pheromone synthesis, chemosensory perception, and physiological and behavioral responses to varied pheromones. In this review, we highlight the genes and pathways that regulate queen pheromone-mediated social communication, discuss the evolutionary changes in genetic systems, and outline prospects of functional studies in sociobiology.

Distinct chemical blends produced by different reproductive castes in the subterranean termite Reticulitermes flavipes

The production of royal pheromones by reproductives (queens and kings) enables social insect colonies to allocate individuals into reproductive and non-reproductive roles. In many termite species, nestmates can develop into neotenics when the primary king or queen dies, which then inhibit the production of additional reproductives. This suggests that primary reproductives and neotenics produce royal pheromones. The cuticular hydrocarbon heneicosane was identified as a royal pheromone in Reticulitermes flavipes neotenics. Here, we investigated the presence of this and other cuticular hydrocarbons in primary reproductives and neotenics of this species, and the ontogeny of their production in primary reproductives. Our results revealed that heneicosane was produced by most neotenics, raising the question of whether reproductive status may trigger its production. Neotenics produced six additional cuticular hydrocarbons absent from workers and nymphs. Remarkably, heneicosane and four of these compounds were absent in primary reproductives, and the other two compounds were present in lower quantities. Neotenics therefore have a distinct 'royal' blend from primary reproductives, and potentially over-signal their reproductive status. Our results suggest that primary reproductives and neotenics may face different social pressures. Future studies of these pressures should provide a more complete understanding of the mechanisms underlying social regulation in termites.

Reproductive Soldier Development Is Controlled by Direct Physical Interactions with Reproductive and Soldier Termites

In eusocial insects (e.g., ants, bees, and termites), the roles of different castes are assigned to different individuals. These castes possess unique phenotypes that are specialized for specific tasks. The acquisition of sterile individuals with specific roles is considered a requirement for social evolution. In termites, the soldier is a sterile caste. In primitive taxa (family Archotermopsidae and Stolotermitidae), however, secondary reproductives (neotenic reproductives) with their mandibles developed into weapons (so-called reproductive soldiers, also termed as soldier-headed reproductives or soldier neotenics) have been reported. To understand the developmental mechanism of this unique caste, it is necessary to understand the environmental cues and developmental processes of reproductive soldiers under natural conditions. Here, we established efficient conditions to induce reproductive soldiers in Zootermopsis nevadensis. Male reproductive soldiers frequently developed after the removal of both the king and soldiers from an incipient colony. Similarly, high differentiation rates of male reproductive soldiers were observed after king-and-soldier separation treatment using wire mesh. However, no male reproductive soldiers were produced without direct interaction with the queen. These results suggest that male reproductive soldier development is repressed by direct physical interactions with both the king and soldiers and facilitated by direct physical interaction with the queen.

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.

Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons

Insect cuticular hydrocarbons (CHCs) consist of complex mixtures of straight-chain alkanes and alkenes, and methyl-branched hydrocarbons. In addition to restricting water loss through the cuticle and preventing desiccation, they have secondarily evolved to serve a variety of functions in chemical communication and play critical roles as signals mediating the life histories of insects. In this review, we describe the physical properties of CHCs that allow for both waterproofing and signaling functions, summarize their roles as inter- and intraspecific chemical signals, and discuss the influences of diet and environment on CHC profiles. We also present advances in our understanding of hydrocarbon biosynthesis. Hydrocarbons are biosynthesized in oenocytes and transported to the cuticle by lipophorin proteins. Recent work on the synthesis of fatty acids and their ultimate reductive decarbonylation to hydrocarbons has taken advantage of powerful new tools of molecular biology, including genomics and RNA interference knockdown of specific genes, to provide new insights into the biosynthesis of hydrocarbons.

Colony-age-dependent variation in cuticular hydrocarbon profiles in subterranean termite colonies

Cuticular hydrocarbons (CHCs) have, in insects, important physiological and ecological functions, such as protection against desiccation and as semiochemicals in social taxa, including termites. CHCs are, in termites, known to vary qualitatively and/or quantitatively among species, populations, castes, or seasons. Changes to hydrocarbon profile composition have been linked to varying degrees of aggression between termite colonies, although the variability of results among studies suggests that additional factors might have been involved. One source of such variability may be colony age, as termite colony demographics significantly change over time, with different caste and instar compositions throughout the life of the colony. We here hypothesize that the intracolonial chemical profile heterogeneity would be high in incipient termite colonies but would homogenize over time as a colony ages and accumulates older workers in improved homeostatic conditions. We studied caste-specific patterns of CHC profiles in Coptotermes gestroi colonies of four different age classes (6, 18, 30, and 42 months). The CHC profiles were variable among castes in the youngest colonies, but progressively converged toward a colony-wide homogenized chemical profile. Young colonies had a less-defined CHC identity, which implies a potentially high acceptance threshold for non-nestmates conspecifics in young colonies. Our results also suggest that there was no selective pressure for an early-defined colony CHC profile to evolve in termites, potentially allowing an incipient colony to merge nonagonistically with another conspecific incipient colony, with both colonies indirectly and passively avoiding mutual destruction as a result.

Pheromonal Regulation of the Reproductive Division of Labor in Social Insects

The reproductive altruism in social insects is an evolutionary enigma that has been puzzling scientists starting from Darwin. Unraveling how reproductive skew emerges and maintains is crucial to understand the reproductive altruism involved in the consequent division of labor. The regulation of adult worker reproduction involves conspecific inhibitory signals, which are thought to be chemical signals by numerous studies. Despite the primary identification of few chemical ligands, the action modes of primer pheromones that regulate reproduction and their molecular causes and effects remain challenging. Here, these questions were elucidated by comprehensively reviewing recent advances. The coordination with other modalities of queen pheromones (QPs) and its context-dependent manner to suppress worker reproduction were discussed under the vast variation and plasticity of reproduction during colony development and across taxa. In addition to the effect of QPs, special attention was paid to recent studies revealing the regulatory effect of brood pheromones. Considering the correlation between pheromone and hormone, this study focused on the production and perception of pheromones under the endocrine control and highlighted the pivotal roles of nutrition-related pathways. The novel chemicals and gene pathways discovered by recent works provide new insights into the understanding of social regulation of reproductive division of labor in insects.

Cooperative policing behaviour regulates reproductive division of labour in a termite

Reproductive conflicts are common in insect societies where helping castes retain reproductive potential. One of the mechanisms regulating these conflicts is policing, a coercive behaviour that reduces direct reproduction by other individuals. In eusocial Hymenoptera (ants, bees and wasps), workers or the queen act aggressively towards fertile workers, or destroy their eggs. In many termite species (order Blattodea), upon the death of the primary queen and king, workers and nymphs can differentiate into neotenic reproductives and inherit the breeding position. During this process, competition among neotenics is inevitable, but how this conflict is resolved remains unclear. Here, we report a policing behaviour that regulates reproductive division of labour in the eastern subterranean termite, Reticulitermes flavipes. Our results demonstrate that the policing behaviour is a cooperative effort performed sequentially by successful neotenics and workers. A neotenic reproductive initiates the attack of the fellow neotenic by biting and displays alarm behaviour. Workers are then recruited to cannibalize the injured neotenic. Furthermore, the initiation of policing is age-dependent, with older reproductives attacking younger ones, thereby inheriting the reproductive position. This study provides empirical evidence of policing behaviour in termites, which represents a convergent trait shared between eusocial Hymenoptera and Blattodea.

Reproductives and eggs trigger worker vibration in a subterranean termite

In insect societies, the presence of reproductives or eggs has been shown to shape several biological traits in the colony members. Social interactions are one of these traits that involve modification of the communication system of the entire colony. Many studies described the role of chemical compounds and dominance behaviors in the presence of reproductive but vibratory behaviors received very few investigations. Yet, vibratory behaviors are ideal candidates, particularly for subterranean species like termites, as they could be quickly transmitted through the substrate and could be very diversified (origin, modulation). Here, we investigated whether the presence of reproductives/eggs affects the vibratory behavior (body-shaking) of workers in the subterranean termite Reticulitermes flavipes. Our results reveal that the presence of reproductives or eggs triggers an increase of workers' body-shaking, independent of their colony of origin after 24 hr. We hypothesize that vibratory communication could be used to transfer information about the presence of reproductives and eggs to the entire colony, suggesting that vibratory behaviors could serve as an important yet neglected mediator of social regulation.

Chemical identification of an aggregation pheromone in the termite Reticulitermes speratus

Social behaviours in termites are regulated by sophisticated chemical communication systems. The majority of subterranean termites continuously forage for new wood resources to expand their nesting areas; an aggregation pheromone is presumed to regulate this process. However, the chemical components of this pheromone have never been determined. We identified the chemical properties of the aggregation pheromone that signals nestmate presence and induces arrest in the termite Reticulitermes speratus. The results of gas chromatography-mass spectrometry analyses and bioassays indicated that R. speratus worker release the pheromone to their nesting site. The pheromone consists of an aromatic compound (2-phenylundecane), cuticular hydrocarbons (pentacosane and heptacosane), fatty acids (palmitic acid and trans-vaccenic acid), and cholesterol; the pheromone induces long-term aggregation at new nesting and feeding sites. Although 2-phenylundecane alone attracted workers, the combination of all six compounds showed greater arrestant activity than 2-phenylundecane alone. This suggests that 2-phenylundecane functions as an attractant, whereas the remaining five components function as arrestants. Our results indicate that foraging worker termites produce a multi-component aggregation pheromone by combining a volatile hydrocarbon and non-volatile lipids with cuticular hydrocarbons. This pheromone enables rapid, long-lasting aggregation of termite workers, which contributes to efficient feeding and colonisation of new wood. Our work furthers the understanding of chemical communication systems underlying social assembly in social insects.

The making of the defensive caste: Physiology, development, and evolution of the soldier differentiation in termites

Termites (Blattodea, Termitoidea, or Isoptera) constitute one of the major lineages of eusocial insects. In termite societies, multiple types of functional individuals, that is, castes, perform divisions of labors to coordinate social behaviors. Among other castes, the soldier caste is distinctive since it is sterile and exclusively specialized into defensive behavior with largely modified morphological features. Therefore, many of the previous studies have been focused on soldiers, in terms of ecology, behavior, and evolution as well as developmental and physiological mechanisms. This article overviews the accumulation of studies especially focusing on the developmental and physiological mechanisms underlying the soldier differentiation in termites. Furthermore, the evolutionary trajectories that have led the acquisition of soldier caste and have diversified the soldier characteristics in association with the social evolution are discussed.

(3R,6E)-nerolidol, a fertility-related volatile secreted by the queens of higher termites (Termitidae: Syntermitinae)

The queens of advanced social insects maintain their reproductive monopoly by using exocrine chemicals. The chemistry of these "queen pheromones" in termites is poorly known. We show that primary queens of four higher termites from the subfamily Syntermitinae (Embiratermes neotenicus, Silvestritermes heyeri, Labiotermes labralis, and Cyrilliotermes angulariceps) emit significant amounts of the sesquiterpene alcohol (E)-nerolidol. It is the dominant analyte in queen body washes; it is present on the surface of eggs, but absent in kings, workers, and soldiers. In E. neotenicus, it is also produced by replacement neotenic queens, in quantities correlated with their fertility. Using newly synthesised (3R,6E)-nerolidol, we demonstrate that the queens of this species produce only the (R) enantiomer. It is distributed over the surface of their abdomen, in internal tissues, and in the haemolymph, as well as in the headspace of the queens. Both (R) and (S) enantiomers are perceived by the antennae of E. neotenicus workers. The naturally occurring (R) enantiomer elicited a significantly larger antennal response, but it did not show any behavioural effect. In spite of technical difficulties encountered in long-term experiments with the studied species, (3R,6E)-nerolidol remains among eventual candidates for the role in queen fertility signalling.

The critical role of primer pheromones in maintaining insect sociality

Primer pheromones play a pivotal role in the biology and social organization of insect societies. Despite their importance, they have been less studied because of the complexity of the required bioassays and, consequently, only a few of them have been chemically identified to date. The major primer pheromones are that of the queen pheromones that regulate reproductive skew and maintain colony cohesion and function. From a theoretical viewpoint, several features regarding the chemistry of queen pheromones can be predicted. They should be generally nonvolatile in order to avoid saturation of the colony space, which might otherwise hamper their perception because of sensory habituation. Accordingly, they should be actively dispersed throughout the colony by workers. The queen pheromone should also be caste-specific, qualitatively different from any worker pheromone, and preferably multicomponent, to allow unequivocal identification of the queen. The bi-potency of the female larvae in social Hymenoptera to become queen or worker necessitates strict regulation over pheromone production. Indeed, in the honeybee, the biosynthetic pathways as well as the genomic expressions are completely disparate between queens and workers. Future advances in chemical analyses, transcriptomics, proteomics, and metabolomics will enrich our understanding of the chemistry, mechanisms, and crucial role that primer pheromones play in social evolution.

2018 Highlights of Urban Entomology

The field of urban entomology is primarily associated with the study of ants, bed bugs, cockroaches, termites, and other occasional invader pests that are found within or near human-made structures. A wide array of peer-reviewed studies were published in 2018. The topics of these articles ranged from genomes and basic biology of urban insects to various applied aspects of pest management. Key findings of these papers are presented and discussed from the perspective of the contributions they make to the discipline of urban entomology. Additionally, potential future research opportunities that are evident from these publications have been outlined.

Do Bumble Bees Produce Brood Pheromones?

Reproductive division of labor, a defining feature of social insects, is often regulated by a combination of behavioral and chemical means. It is hypothesized that behavioral interactions play a more important role in regulating reproduction of primitive eusocial species, while pheromones are typically used by large sized, advanced eusocial species. Here we examined if worker reproduction in the primitively eusocial species Bombus impatiens is regulated by brood pheromones. We recently demonstrated that worker egg laying in this species is inhibited by young larvae and triggered by pupae. However, the mechanism by which the brood communicates its presence and whether brood or hunger pheromones are involved remain unknown. We found that workers were behaviorally attracted to pupae over larvae or control in a choice experiment, in line with their reproductive interests. However, odors from larvae or pupae were insufficient to inhibit worker reproduction. We further show that the youngest larvae are particularly vulnerable to starvation, however, despite a slight attraction and fewer eggs laid by workers in the presence of starved compared with fed larvae, these effects were insignificant. Our study demonstrates that workers can differentiate between larvae and pupae, but not between starved and fed larvae based on olfactory information. However, these signals alone do not explain the reduction in worker egg laying previously found. Bumble bee workers may use information from multiple sources or rely solely on behavioral interactions with brood and other females to make decisions about reproduction, in line with their small colony size and simple social organization.

The oral gland, a new exocrine organ of termites

Termites have a rich set of exocrine glands. These glands are located all over the body, appearing in the head, thorax, legs and abdomen. Here, we describe the oral gland, a new gland formed by no more than a few tens of Class I secretory cells. The gland is divided into two secretory regions located just behind the mouth, on the dorsal and ventral side of the pharynx, respectively. The dominant secretory organelle is a smooth endoplasmic reticulum. Secretion release is under direct control of axons located within basal invaginations of the secretory cells. The secretion is released through a modified porous cuticle located at the mouth opening. We confirmed the presence of the oral gland in workers and soldiers of several wood- and soil-feeding species of Rhinotermitidae and Termitidae, suggesting a broader distribution of the oral gland among termites. The oral gland is the smallest exocrine gland described in termites so far. We hypothesise that the oily secretion can either ease the passage of food or serve as a primer pheromone.

Role of Cuticular Hydrocarbons in German Cockroach (Blattodea: Ectobiidae) Aggregation Behavior

Aggregation can be adaptive by providing protection from predators, facilitating thermoregulation, and expediting the location of food, shelter, and mates. German cockroaches Blattella germanica L. (Blattodea: Ectobiidae), are obligatory commensals in human-built structures, where they aggregate in crevices during the day. The source of the aggregation pheromone that drives this behavior and its chemical identity remain unclear. Cuticular hydrocarbons (CHCs) in feces have been proposed to serve as aggregation pheromone, but this function has not been investigated in relation to visual and tactile cues that mediate aggregation. Our objective was to delineate how CHCs in the feces and on the cockroach body operate in conditions that reflect the German cockroach's ecology-either applied to shelters, representing fecal deposition, or to previously extracted cockroaches, representing shelter co-habitation with other cockroaches. Cockroaches and feces-conditioned filter papers were extracted, CHCs were purified by flash chromatography, and two-choice behavior assays were performed with first instar nymphs. Our results confirmed that nymphs preferred to rest within feces-conditioned shelters. However, purified CHCs did not elicit more aggregation than solvent-treated control shelters. Nymphs significantly preferred to rest in shelters that contained a CHC-free dead female, but the addition of CHCs to the female did not enhance aggregation. Nymphs preferred to aggregate with the CHC-free female over CHC-treated shelters. Finally, a methanol extract of feces was highly effective at eliciting aggregation, contesting previous reports that fecal CHCs serve as aggregation pheromone. We assert that CHCs play a minor, if any, role in the aggregation behavior of German cockroaches.

Queen and king recognition in the subterranean termite, Reticulitermes flavipes: Evidence for royal recognition pheromones

Royal recognition is a central feature of insect societies, allowing them to maintain the reproductive division of labor and regulate colony demography. Queen recognition has been broadly demonstrated and queen recognition pheromones have been identified in social hymenopterans, and in one termite species. Here we describe behaviors that are elicited in workers and soldiers by neotenic queens and kings of the subterranean termite, Reticulitermes flavipes, and demonstrate the chemical basis for the behavior. Workers and soldiers readily perform a lateral or longitudinal shaking behavior upon antennal contact with queens and kings. When royal cuticular chemicals are transferred to live workers or inert glass dummies, they elicit antennation and shaking in a dose-dependent manner. The striking response to reproductives and their cuticular extracts suggests that royal-specific cuticular compounds act as recognition pheromones and that shaking behavior is a clear and measurable queen and king recognition response in this termite species.

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.

Unbalanced biparental care during colony foundation in two subterranean termites

Parental care is a major component of reproduction in social organisms, particularly during the foundation steps. Because investment into parental care is often costly, each parent is predicted to maximize its fitness by providing less care than its partner. However, this sexual conflict is expected to be low in species with lifelong monogamy, because the fitness of each parent is typically tied to the other's input. Somewhat surprisingly, the outcomes of this tug-of-war between maternal and paternal investments have received important attention in vertebrate species, but remain less known in invertebrates. In this study, we investigated how queens and kings share their investment into parental care and other social interactions during colony foundation in two termites with lifelong monogamy: the invasive species Reticulitermes flavipes and the native species R. grassei. Behaviors of royal pairs were recorded during six months using a non-invasive approach. Our results showed that queens and kings exhibit unbalanced investment in terms of grooming, antennation, trophallaxis, and vibration behavior. Moreover, both parents show behavioral differences toward their partner or their descendants. Our results also revealed differences among species, with R. flavipes exhibiting shorter periods of grooming and antennation toward eggs or partners. They also did more stomodeal trophallaxis and less vibration behavior. Overall, this study emphasizes that despite lifelong monogamy, the two parents are not equally involved in the measured forms of parental care and suggests that kings might be specialized in other tasks. It also indicates that males could play a central, yet poorly studied role in the evolution and maintenance of the eusocial organization.

Genomic Signals of Adaptation towards Mutualism and Sociality in Two Ambrosia Beetle Complexes

Mutualistic symbiosis and eusociality have developed through gradual evolutionary processes at different times in specific lineages. Like some species of termites and ants, ambrosia beetles have independently evolved a mutualistic nutritional symbiosis with fungi, which has been associated with the evolution of complex social behaviors in some members of this group. We sequenced the transcriptomes of two ambrosia complexes (Euwallacea sp. near fornicatus⁻Fusarium euwallaceae and Xyleborus glabratus⁻Raffaelea lauricola) to find evolutionary signatures associated with mutualism and behavior evolution. We identified signatures of positive selection in genes related to nutrient homeostasis; regulation of gene expression; development and function of the nervous system, which may be involved in diet specialization; behavioral changes; and social evolution in this lineage. Finally, we found convergent changes in evolutionary rates of proteins across lineages with phylogenetically independent origins of sociality and mutualism, suggesting a constrained evolution of conserved genes in social species, and an evolutionary rate acceleration related to changes in selective pressures in mutualistic lineages.

Identification and Enantiodivergent Synthesis of (5 Z,9 S)-Tetradec-5-en-9-olide, a Queen-Specific Volatile of the Termite Silvestritermes minutus

The queens of social insects differ from sterile colony members in many aspects of their physiology. Besides adaptations linked with their specialization for reproduction and extended lifespan, the queens also invest in the maintenance of their reproductive dominance by producing exocrine chemicals signaling their presence to the nestmates. The knowledge of the chemistry of queen-specific cues in termites is scarce. In addition to the contact recognition based on cuticular hydrocarbons, long-range signals mediated by volatiles are expected to participate in queen signaling, especially in populous colonies of higher termites (Termitidae). In queens of the higher termite Silvestritermes minutus (Syntermitinae), we have detected a previously undescribed volatile. It is present in important quantities on the body surface and in the headspace, ovaries, and body cavity. MS and GC-FTIR data analyses led us to propose the structure of the compound to be a macrolide 10-pentyl-3,4,5,8,9,10-hexahydro-2 H-oxecin-2-one. We performed enantiodivergent syntheses of two possible enantiomers starting from enantiopure ( S)-glycidyl tosylate. The synthetic sequence involved macrolide-closing metathesis quenched with a ruthenium scavenging agent. The absolute and relative configuration of the compound was assigned to be (5 Z,9 S)-tetradec-5-en-9-olide. Identification and preparation of the compound allow for investigation of its biological significance.

Identification of a queen and king recognition pheromone in the subterranean termite Reticulitermes flavipes

Chemical communication is fundamental to success in social insect colonies. Species-, colony-, and caste-specific blends of cuticular hydrocarbons (CHCs) and other chemicals have been well documented as pheromones, mediating important behavioral and physiological aspects of social insects. More specifically, royal pheromones used by queens (and kings in termites) enable workers to recognize and care for these vital individuals and maintain the reproductive division of labor. In termites, however, no royal-recognition pheromones have been identified to date. In the current study, solvent extracts of the subterranean termite Reticulitermes flavipes were analyzed to assess differences in cuticular compounds among castes. We identified a royal-specific hydrocarbon-heneicosane-and several previously unreported and highly royal enriched long-chain alkanes. When applied to glass dummies, heneicosane elicited worker behavioral responses identical to those elicited by live termite queens, including increased vibratory shaking and antennation. Further, the behavioral effects of heneicosane were amplified when presented with nestmate termite workers' cuticular extracts, underscoring the importance of chemical context in termite royal recognition. Thus, heneicosane is a royal-recognition pheromone that is active in both queens and kings of R. flavipes The use of heneicosane as a queen and king recognition pheromone by termites suggests that CHCs evolved as royal pheromones ∼150 million years ago, ∼50 million years before their first use as queen-recognition pheromones in social Hymenoptera. We therefore infer that termites and social Hymenoptera convergently evolved the use of these ubiquitous compounds in royal recognition.