Dufour’s gland possible role in the evolution of sting morphology and function in hover wasps (Hymenoptera Stenogastrinae)

The sting is the most effective defense of social Hymenoptera against vertebrate predators but in the hover wasps (subfamily Stenogastrinae) it is scarcely used. In these wasps a quite enlarged Dufour’s gland and the extensive use of its secretion in the peculiar rearing of the larvae and defense determined important morphological modifications of the sting structure. Connecting anatomical and morphological data with behavioral observations we determined that in these wasps the Dufour’s gland secretion is attached to the egg during oviposition but can be also channeled to the outside via the sting when it is collected by adult females for larval rearing or construction of the nest ant guards. The anatomical modifications of the sting reduced the function of the sting as a defensive weapon in hover wasps.     

Exocrine gland secretions of virgin queens of five bumblebee species (Hymenoptera: Apidae, Bombini)

Secretions of three different glands (mandibular gland, labial gland, and Dufour's gland) of virgin queens of five bumblebee species (Bombus lucorum, B. lapidarius, B. hypnorum, B. pascuorum, and B. terrestris) were analysed. Around 200 compounds were identified in the secretions. The compositions of the secretions of labial and mandibular glands were species-specific. Dufour's gland of all species produced mainly hydrocarbons, both saturated and unsaturated, the proportions of which differed quantitatively between the species studied.     

The role of Dufour's gland secretions in bees

ABSTRACT. Dufour's gland of bees is often hypertrophied and an extremely rich source of diverse natural products. In the ground-dwelling bees the secretion is mostly used for lining the brood cell with a hydrophobic lining. Whereas in several species the secretion is smeared on the cell walls without any modification, in others the hydrophobic lining is formed only after a chemical transformation of the secretion. The diversity of the chemical means by which hydrophobicity of the brood cells is achieved suggests that it has evolved repeatedly in the bees. In addition to lining their brood cells, several species use Dufour's gland secretion to mark their nest entrance. Analyses of single glands from various species reveal that each bee possesses its own individual composition, expressed in specific relative amounts of each component. Interestingly in the social halictid Evylaeus malachurum , nestmates (considered as sisters) are more similar to each other than non-related bees. The possible functional evolution of the glandular exudate from structural functions to communication and its implications for our understanding of eusociality in bees, is discussed.     

Behavioral responses to the alarm pheromone of the ant Camponotus obscuripes (Hymenoptera: Formicidae)

The alarm pheromone of the ant Camponotus obscuripes (Formicinae) was identified and quantified by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Comparisons between alarm pheromone components and extracts from the major exocrine gland of this ant species revealed that the sources of its alarm pheromone are Dufour's gland and the poison gland. Most components of Dufour's gland were saturated hydrocarbons. n-Undecane comprised more than 90% of all components and in a single Dufour's gland amounted to 19 microg. n-Decane and n-pentadecane were also included in the Dufour's gland secretion. Only formic acid was detected in the poison gland, in amounts ranging from 0.049 to 0.91 microl. This ant species releases a mixture of these substances, each of which has a different volatility and function. When the ants sensed formic acid, they eluded the source of the odor; however, they aggressively approached odors of n-undecane and n-decane, which are highly volatile. In contrast, n-pentadecane, which has the lowest volatility among the identified compounds, was shown to calm the ants. The volatilities of the alarm pheromone components were closely related to their roles in alarm communication. Highly volatile components vaporized rapidly and spread widely, and induced drastic reactions among the ants. As these components became diluted, the less volatile components calmed the excited ants. How the worker ants utilize this alarm communication system for efficient deployment of their nestmates in colony defense is also discussed herein.     

Chemical defense by the native winter ant (Prenolepis imparis) against the invasive Argentine ant (Linepithema humile)

The invasive Argentine ant (Linepithema humile) is established worldwide and displaces native ant species. In northern California, however, the native winter ant (Prenolepis imparis) persists in invaded areas. We found that in aggressive interactions between the two species, P. imparis employs a potent defensive secretion. Field observations were conducted at P. imparis nest sites both in the presence and absence of L. humile. These observations suggested and laboratory assays confirmed that P. imparis workers are more likely to secrete when outnumbered by L. humile. Workers of P. imparis were also more likely to secrete near their nest entrances than when foraging on trees. One-on-one laboratory trials showed that the P. imparis secretion is highly lethal to L. humile, causing 79% mortality. The nonpolar fraction of the secretion was chemically analyzed with gas chromatography/mass spectrometry, and found to be composed of long-chain and cyclic hydrocarbons. Chemical analysis of dissected P. imparis workers showed that the nonpolar fraction is derived from the Dufour's gland. Based on these conclusions, we hypothesize that this chemical defense may help P. imparis to resist displacement by L. humile.     

Host-parasite relationships in six species ofSphecodes bees and their halictid hosts: Nest intrusion,intranidal behavior,and Dufour's gland volatiles (Hymenoptera: Halictidae)

Nest invasion behavior was studied in six kleptoparasiticSphecodes species at four nesting sites of their respective social and solitary hosts.Sphecodes females preferred to enter unguarded nests. Nest intruding strategies observed in the differentSphecodes species did not depend on whether host species were solitary or social, as long as the nesting cycle of a social host was in the solitary stage (i.e., a single host female). Observation of intranidal behavior revealed thatSphecodes monilicornis females kill all host individuals within an usurped nest. They stay in the nest for several hours, laying eggs in adequately provisioned brood cells. Gas chromatography-mass spectrometry analyses of Dufour's gland secretions revealed species-specific compositions. Qualitative comparisons of whole patterns and quantitative comparisons considering the predominant hydrocarbons common to both host and parasite contradict the hypothesis of chemical mimetism, a mechanism supposed to permit parasite intrusion by qualitatively similar odor bouquets in host and parasite females.     

A role of the Dufour's gland in the dominance interactions of the paper wasp,Polistes fuscatus (Hymenoptera: Vespidae)

The Dufour's gland of the paper wasp, Polistes fuscatus,is a source of the cues used by dominant females to recognize the eggs laid by subordinates or nonnestmates on pre (worker)-emergence nests. When dominant wasps were presented with an egg covered with either (1) the Dufour's gland extract of a subordinate cofoundress, (2) the extract of an egg from the same subordinate, or (3) the solvent alone, the dominant female destroyed and replaced the eggs covered with the Dufour's extract significantly more frequently than the other eggs. Eggs with the extract of a nonnestmate's Dufour's gland were also eaten significantly more frequently than those with the solvent. Given similar choices, subordinates did not destroy any eggs. The Dufour's gland appears to have little or no role in communicating dominance directly among aggressively interacting cofoundresses.     

Prey capture behavior in an arboreal African ponerine ant

I studied the predatory behavior of Platythyrea conradti, an arboreal ponerine ant, whereas most species in this subfamily are ground-dwelling. The workers, which hunt solitarily only around dusk, are able to capture a wide range of prey, including termites and agile, nocturnal insects as well as diurnal insects that are inactive at that moment of the Nyctemeron, resting on tree branches or under leaves. Prey are captured very rapidly, and the antennal palpation used by ground-dwelling ponerine species is reduced to a simple contact; stinging occurs immediately thereafter. The venom has an instant, violent effect as even large prey (up to 30 times the weight of a worker) never struggled after being stung. Only small prey are not stung. Workers retrieve their prey, even large items, singly. To capture termite workers and soldiers defending their nest entrances, ant workers crouch and fold their antennae backward. In their role as guards, the termites face the crouching ants and end up by rolling onto their backs, their legs batting the air. This is likely due to volatile secretions produced by the ants' mandibular gland. The same behavior is used against competing ants, including territorially-dominant arboreal species that retreat further and further away, so that the P. conradti finally drive them from large, sugary food sources.     

Honeybee egg-laying workers mimic a queen signal

Summary. In the honeybee, Dufour's gland secretion is caste specific and constitutes a component of the multi-sourced queen signal. As predicted, it is attractive to workers, which form a retinue around the scented source. Bioassays reveal the ester fraction and not the hydrocarbons to be the active constituents. This function of the esters was corroborated by assays with the synthetic queen-esters mixture, which successfully mimicked the queen's secretion. As predicted from the queen-like secretion exhibited by egg-laying workers, their glandular secretion was also attractive to nestmates, albeit to a lesser degree than that of the queen; while that of non-egg-laying workers was totally inactive. The evolution of the multiple queen signals in honeybees can be regarded as a component in an arms race between queen and workers. We hypothesize that in response to a reduced sensitivity to a certain queen signal, queen honeybees were selected to develop an alternative signaling-source. Dufour's gland seems to be one of these sources.     

An evaluation of the possible adaptive function of fungal brood covering by Attine ants

Fungus-growing ants (Myrmicinae: Attini) live in an obligate symbiotic relationship with a fungus that they rear for food, but they can also use the fungal mycelium to cover their brood. We surveyed colonies from 20 species of fungus-growing ants and show that brood-covering behavior occurs in most species, but to varying degrees, and appears to have evolved shortly after the origin of fungus farming, but was partly or entirely abandoned in some genera. To understand the evolution of the trait we used quantitative phylogenetic analyses to test whether brood-covering behavior covaries among attine ant clades and with two hygienic traits that reduce risk of disease: mycelial brood cover did not correlate with mutualistic bacteria that the ants culture on their cuticles for their antibiotics, but there was a negative relationship between metapleural gland grooming and mycelial cover. A broader comparative survey showed that the pupae of many ant species have protective cocoons but that those in the subfamily Myrmicinae do not. We therefore evaluated the previously proposed hypothesis that mycelial covering of attine ant brood evolved to provide cocoon-like protection for the brood.     

A latitudinal gradient in intensity of applying ant-repellent substance to the nest petiole in paper wasps (Hymenoptera: Vespidae)

Summary Observations on pre-emergence, single-foundress colonies of Japanese paper wasps (Polistes) revealed that there was a latitudinal gradient in intensity of application of an ant-repellent substance (secreted by the metasomal sternum VI glands) to the nest petiole. Thus the lower the latitude, the more frequently a foundress rubbed ant repellent onto the nest petiole. Estimation of potential ant predation on wasp brood using bait traps showed that there was a positive correlation between the frequency of rubbing and potential predation pressure from ants which are guided predominantly by substrate cues for foraging. There was also a latitudinal gradient in the degree of temporal association of rubbing behavior with foraging: the lower the latitude, the more closely foundress departure from the nest was associated with rubbing. Enlargement of the nest petiole by applying oral secretion potentially obliterated previous coats of ant repellent; however, this behavior was not always followed by rubbing behavior. The ant-repellent chemical barrier around the nest petiole may have evolved in tropical regions of the world as a defense against ant predation on wasp brood. I argue that as ant predation pressure diminishes towards the cooler regions, so does selection maintaining the behavioral sequence where foundress departure from the nest is preceded by rubbing behavior.     

Biology and social behaviour of three species ofAnischnogaster (Vespidae,Stenogastrinae) in Papua New Guinea

Summary Level of social organization, adult behaviour, size and development of the brood in three species ofAnischnogaster are described. The normal colony size in all the three species was one female per nest, and colony size never exceeded two females per nest. The social interactions, which were only observed in one species, did not include any marked dominance behaviour, but there was clear caste differentiation, with the older female guarding the nest while the younger female foraged for food. InAnischnogaster sp. A only some eggs and larvae have abdominal secretion, while no secretion at all was found on the eggs and larvae ofA. laticeps. In spite of this, the Dufour's gland was found to be well developed. The significance of this is discussed. Females ofA. laticeps were found to fall into two groups distinguished by the length of the sting. The larvae seem quite similar to those of other Stenogastrinae and have, apparently, only four instars.     

Chemistry and morphology of the tergal gland of freeliving adult Aleocharinae (Coleoptera: Staphylinidae) and its phylogenetic significance

Abstract. Morphology and chemistry of the tergal gland, an abdominal defensive gland of the Staphylinidae subfamily Aleocharinae, is studied comparatively in twenty-two species of ten Central European tribes. To determine trends in the morphological evolution of the tergal gland the results are compared with well-known evolutionary trends of gland systems of other insects. The possible chemical evolution of the gland secretion is proposed by considering the biosynthesis of the different secretion compounds and by testing their biological efficiency on Calliphora larvae (irritancy, mortality). The morphological evolution probably proceeded from a small reservoir with only a few glandular cells D₁ (primitive) to a large and bilobed reservoir with a great number of glandular cells D₁ (advanced). In the chemistry of the quinone-containing gland secretion, long-chain fatty acids as solvents in primitive species were probably replaced by short-chain fatty acids (derived condition). Most advanced species also use hydrocarbons and aldehydes as solvents. With reference to these results, both a statistical (Jaccard-coefficient) and a cladistic analysis are performed to test previous ideas on the phylogeny of the Aleocharinae.     

The perception of genetic similarity by the solitary parthenogenetic parasitoid Venturia canescens, and its effects on the occurrence of superparasitism

Observations of oviposition patterns adopted by uniparental lines of the solitary parthenogenetic endoparasitoid Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae) reveal that the occurrence of superparasitism is influenced by the genealogical relationship between adult wasps and conspecific progeny which they encounter within parasitized hosts (larvae of the Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae)): the closer the relationship, the lower the occurrence of superparasitism. This behaviour has an adaptive interpretation because it allows Venturia to avoid selective penalties incurred when larval offspring compete with genetically similar progeny. Venturia's ability to discriminate between her own eggs, those of her relatives, and those of other conspecifics is mediated by a chemical marker produced by Dufour's gland, an accessory of the adult female's reproductive system. This conclusion is supported by chemical analyses which reveal that, while Dufour's glands from unrelated females show highly significant variation between the spectra of volatile hydrocarbons contained in their respective secretions, closely-related females show negligible differences in their chemical constitutions. These findings lend further weight to current theory that superparasitism can be deliberately deployed as an adaptive part of a wasp's behavioural repertoire, and also identify the physiological mechanism by which such an oviposition response may be achieved.     

Release from prey preservation behavior via prey switch allowed diversification of cuticular hydrocarbon profiles in digger wasps

The cuticle of insects is covered by a layer of hydrocarbons (CHC), whose original function is the protection from desiccation and pathogens. However, in most insects CHC profiles are species specific. While this variability among species was largely linked to communication and recognition functions, additional selective forces may shape insect CHC profiles. Here, we show that in Philanthinae digger wasps (Crabronidae) the CHC profile coevolved with a peculiar brood‐care strategy. In particular, we found that the behavior to embalm prey stored in the nest with hydrocarbons is adaptive to protect larval food from fungi in those species hunting for Hymenoptera. The prey embalming secretion is identical in composition to the alkene‐dominated CHC profile in these species, suggesting that their profile is adaptively conserved for this purpose. In contrast, prey embalming is not required in those species that switched to Coleoptera as prey. Released from this chemical brood‐care strategy, Coleoptera‐hunting species considerably diversified their CHC profiles. Differential needs to successfully protect prey types used as larval food have thus driven the diversification of CHCs profiles of female Philanthinae wasps. To the best of our knowledge, this is the first evidence of a direct link between selection pressure for food preservation and CHC diversity.     

THE VULNERABILITY OF POLLEN AND FUNGAL SPORES TO ANT SECRETIONS: EVIDENCE AND SOME EVOLUTIONARY IMPLICATIONS

The quality of Brassica and Acacia pollen is adversely affected by exposure to secretions drawn from the metapleural gland of the ant Myrmecia nigriscapa. Ultrastructural studies show that the apparently lipoidal secretions destroy both the plasma membranes and those of the cytoplasmic organelles. Exposure to the integument of this ant prevents the normal hydration of pollen grains. Exposure to the integument of a species of Camponotus, which does not appear to possess metapleural gland openings, also reduces pollen quality. Mycelial development in seven species of soil-dwelling fungi is inhibited by secretions of the metapleural gland. Two fungal species that are normally entomogenous are most vulnerable to the secretion. It is suggested that the metapleural gland is producing a powerful antibiotic and that the antibiosis that results from its activity, on one hand, alleviates the attacks of microorganisms in nest cavities, while on the other, incidentally kills pollen grains, possibly blocking the evolution of ant pollination systems.     

The origin and evolution of social life in the Stenogastrinae (Hymenoptera,Vespidae)

The Stenogastrinae are a subfamily of the Vespidae. The main difference between these and other social wasps (Polistinae and Vespinae) is a jelly-like substance that the Stenogastrinae secrete from the Dufour 's gland and use in many functions of their biology. It is suggested that this substance greatly contributed to the evolution of social life in these wasps by making it possible to nourish the brood with liquid food and store it in the nest, thus favoring also the evolution of the behavioral mechanisms which facilitated interactions between adults. Social organization of the colonies may have been kept at a low level through a basic system of continuous temporary helper replacement, while the evolution of large colonies was restrained, as well as by the poor quality of construction material, low egg-laying capacity and limited production of abdominal substance, imperfect social regulatory mechanisms, and the absence of defensive mechanisms of the colonies against large predators.     

Correlation between mandibular gland secretion and cuticular hydrocarbons in the stingless bee Melipona quadrifasciata

We investigated whether Melipona quadrifasciata worker mandibular gland secretions contribute directly to their cuticular hydrocarbon profile. The mandibular gland secretion composition and cuticular surface compounds of newly emerged worker bees, nurse bees, and foragers were determined by gas chromatography and mass spectrometry and compared. Both the mandibular gland secretions and the cuticular surface compounds of all worker stages were found to be composed almost exclusively of hydrocarbons. Although the relative proportion of hydrocarbons from the cuticular surface and gland secretion was statistically different, there was a high similarity in the qualitative composition between these structures in all groups of bees.     

Chemical composition of the poison apparatus secretions of the African weaver ant, Oecophylla longinoda, and their role in behaviour

ABSTRACT. Major workers of Oecophylla longinoda emit venom from the tip of the abdomen, as it is brought immediately above the head. The sources of the venom are (a) the poison gland, which contains formic acid, and (b) Dufour's gland, which contains hydrocarbons, including n-undecane and other n-alkanes, 4-tridecene, 8-heptadecene and 4, 7-heptadecadiene. The venom elicits a 'mass attack' response in other major workers. Formic acid and n-undecane presented together experimentally also evoke this response, the mixture being considerably more effective than either compound tested separately. These compounds act in combination with the mandibular gland secretions to form a complex alarm/defence system.     

Queen-signal modulation of worker pheromonal composition in honeybees

Worker sterility in honeybees is neither absolute nor irreversible. Whether under queen or worker control, it is likely to be mediated by pheromones. Queen-specific pheromones are not exclusive to queens; workers with activated ovaries also produce them. The association between ovarian activation and queen-like pheromone occurrence suggests the latter as providing a reliable signal of reproductive ability. In this study we investigated the effect of queen pheromones on ovary development and occurrence of queen-like esters in workers' Dufour's gland. Workers separated from the queenright compartment by a double mesh behaved like queenless workers, activating their ovaries and expressing a queen-like Dufour's gland secretion, confirming that the pheromones regulating both systems are non-volatile. Workers with developed ovaries produced significantly more secretion than sterile workers, which we attribute primarily to increased ester production. Workers separated from the queenright compartment by a single mesh displayed a delayed ovarian development, which we attribute to interrupted transfer of the non-volatile pheromone between compartments. We suggest that worker expression of queen-like characters reflects a queen-worker arms race; and that Dufour's gland secretion may provide a reliable signal for ovarian activation. The associative nature between ovary development and Dufour's gland ester production remains elusive.