Chemical alarm and defence in the oribatid mite Collohmannia gigantea (Acari: Oribatida)

The multicomponent oil gland secretion of Collohmannia gigantea, a middle-derivative mixonomatan oribatid mite, is demonstrated to possess alarm pheromonal and allomonal properties. Four components of the secretion, namely the monoterpenes neryl formate, neral, geranial and the aromatic 2-hydroxy- 6-methyl-benzaldehyde (2,6-HMBD), showed moderate to strong alarm pheromonal activity in adult mites. Naturally elicited response is due to neral (about 50% of the secretion) and probably 2,6-HMBD (only 5% of the secretion, but strong alarm pheromonal activity). This is the second report of an alarm pheromone in Oribatida. Tridecane and pentadecane (=the hydrocarbon fraction of the secretion) did not evoke evident behavioural reactions, and most likely serve as solvents and spreading agents for the pheromonal-active components. Alarm reactions were characterized by a short recognition phase (waving movements with legs I), followed by shrinking back and panic escape from the scent source. In addition, all six components of the oil gland secretion, including the hydrocarbons, exhibited strong allomonal properties against a model oribatid predator, the scydmaenid beetle, Euconnus (Tetramelus) oblongus. Considering the widespread semiochemical properties of oil gland secretions in astigmatid mites (=a highly derivative oribatid group), these results furnish evidence for a phylogenetically early origin of defensive and communicative roles of oil gland secretions in oribatids. These roles include alarm communication, defence and the production of anti-fungal compounds.     

Expanding the ‘enemy-free space’ for oribatid mites: evidence for chemical defense of juvenile Archegozetes longisetosus against the rove beetle Stenus juno

Adult oribatid mites are thought to live functionally in ‘enemy-free space’ due to numerous morphological and chemical defensive strategies. Most juvenile oribatid mites, however, lack hardened cuticles and are thus thought to be under stronger predation pressure. On the other hand, the majority of oribatids have exocrine oil glands in all developmental stages, possibly rendering chemical defense the crucial survival strategy in juvenile Oribatida. We manipulated tritonymphs of the model oribatid mite Archegozetes longisetosus to completely discharge their oil glands and offered these chemically disarmed specimens to the polyphagous rove beetle Stenus juno. Disarmed specimens were easily consumed. By contrast, specimens with filled oil glands were significantly protected, being rejected by the beetles. This is the first direct evidence that oil gland secretions provide soft-bodied juvenile oribatids with chemical protection against large arthropod predators.     

Discrimination of <Emphasis Type="Italic">Oribotritia</Emphasis> species by oil gland chemistry (Acari,Oribatida)

The chemical composition of secretions from opisthonotal (oil) glands in four species of the oribatid mite genus Oribotritia (Mixonomata, Euphthiracaroidea, Oribotritiidae) was compared by means of gas chromatography—mass spectrometry. The secretions of all, O. banksi (from North America) and three Austrian oribotritiids (O. berlesei, O. hermanni, O. storkani), are shown to be based on certain unusual compounds, the iridoid monoterpenes chrysomelidial and epi-chrysomelidial and the diterpene β-springene. These components probably represent general chemical characteristics of oribotriid oil glands. Their relative abundance in the secretions along with further components (mainly saturated and unsaturated C₁₃-, C₁₅-, C₁₇-hydrocarbons, and the tentatively identified octadecadienal) led to well-distinguishable, species-specific oil gland secretions profiles. In addition a reduced set of “Astigmata compounds” (sensu Sakata and Norton in Int J Acarol 27:281–291, 2001)—namely the two monoterpenes neral and geranial—could be detected in extracts of O. banksi nevertheless indicating the classification of euphthiracaroids within the (monophyletic) group of “Astigmata compounds-bearing”-Oribatida. These compounds are considered to be apomorphically reduced in all Austrian species. Our findings emphasize the potential of chemosystematics using oil gland secretion profiles in the discrimination of morphologically very similar, syntopically living or even cryptic oribatid species.     

Preen oil and bird fitness: a critical review of the evidence

The uropygial gland is a holocrine complex exclusive to birds that produces an oleaginous secretion (preen oil) whose function is still debated. Herein, I examine critically the evidence for the many hypotheses of potential functions of this gland. The main conclusion is that our understanding of this gland is still in its infancy. Even for functions that are considered valid by most researchers, real evidence is scarce. Although it seems clear that preen oil contributes to plumage maintenance, we do not know whether this is due to a role in reducing mechanical abrasion or in reducing feather degradation by keratinophilic organisms. Evidence for a function against pathogenic bacteria is mixed, as preen oil has been demonstrated to act against bacteria in vitro, but not in vivo. Nor is it clear whether preen oil can combat pathogenic bacteria on eggshells to improve hatching success. Studies on the effect of preen oil against dermatophytes are very scarce and there is no evidence of a function against chewing lice. It seems clear, however, that preen oil improves waterproofing, but it is unclear whether this acts by creating a hydrophobic layer or simply by improving plumage structure. Several hypotheses proposed for the function of preen oil have been poorly studied, such as reduction of drag in flight. Similarly, we do not know whether preen oil functions as repellent against predators or parasites, makes birds unpalatable, or functions to camouflage birds with ambient odours. On the other hand, a growing body of work shows the important implications of volatiles in preen oil with regard to social communication in birds. Moreover, preen oil clearly alters plumage colouration. Finally, studies examining the impact of preen oil on fitness are lacking, and the costs or limitations of preen‐oil production also remain poorly known. The uropygial gland appears to have several non‐mutually exclusive functions in birds, and thus is likely to be subject to several selective pressures. Therefore, future studies should consider how the inevitable trade‐offs among different functions drive the evolution of uropygial gland secretions.     

The cephalic labial gland secretions of two socially parasitic bumblebees Bombus hyperboreus (Alpinobombus) and Bombus inexspectatus (Thoracobombus) question their inquiline strategy

Social parasitic Hymenopterans have evolved morphological, chemical, and behavioral adaptations to overcome the sophisticated recognition and defense systems of their social host to invade host nests and exploit their worker force. In bumblebees, social parasitism appeared in at least 3 subgenera independently: in the subgenus Psithyrus consisting entirely of parasitic species, in the subgenus Alpinobombus with Bombus hyperboreus, and in the subgenus Thoracobombus with B. inexspectatus. Cuckoo bumblebee males utilize species‐specific cephalic labial gland secretions for mating purposes that can impact their inquiline strategy. We performed cephalic labial gland secretions in B. hyperboreus, B. inexspectatus and their hosts. Males of both parasitic species exhibited high species specific levels of cephalic gland secretions, including different main compounds. Our results showed no chemical mimicry in the cephalic gland secretions between inquilines and their host and we did not identify the repellent compounds already known in other cuckoo bumblebees.     

Histochemical analysis of accessory genital gland secretions in female Pimpla turionellae L. (Hymenoptera: Ichneumonidae)

The secretions produced by the 3 accessory glands of the female genital tract of Pimpla turionellae were investigated histochemically. The uterus gland secretion was identified as a mixture of hyaluronic acid and lipoprotein, that of the poison gland as a neutral mucoprotein. The product of the alkaline gland (Dufour's gland) consists of lecithin and a cholesterol ester. Pimpla females, as parasites of Lepidoptera pupae, inject these secretions into the host hemocoel during oviposition, thus preventing hemocytic encapsulation of their eggs. The physiological functions of the secretions are briefly discussed.     

Ontogenetic changes in the chemistry and morphology of oil glands in Hermannia convexa (Acari: Oribatida)

As a first example for the chemistry of oil gland secretions in the Hermannioidea (one of the three superfamilies of desmonomatan Oribatida), the oil gland secretion of Hermannia convexa was investigated by gas chromatography–mass spectrometry. Hexane extracts of all juvenile stages showed a multicomponent chromatographic pattern, mainly consisting of well-known oil gland secretion components such as neral, geranial, -acaridial and the unsaturated C17-hydrocarbons, 6,9-heptadecadiene and 8-heptadecene. The secretion profiles of juveniles varied slightly between samples of two different collections, namely in the presence of -acaridial and 8-heptadecene. Furthermore, a minor component, identified as 1,8-cineole (= eucalyptol) and hitherto not known from oil gland secretions of other species, was recorded in both juvenile and adult extracts. In adult profiles, 1,8-cineole, in low amounts, represented the only detectable component; thus, their profiles fundamentally differed from those of juveniles. A subsequent histological investigation revealed well developed oil glands in all juvenile stages, but degenerated oil glands in adults, consistent with the chemical data. So far, apart from H. convexa, degeneration of oil glands in the course of ontogenetic development is only known from a brachypylid species; on the other hand, chemical oil gland-polymorphism between juveniles and adults may occur in closely related Nothridae while it does not occur in oil glands of early- and middle-derivative Oribatida (Parhyposomata, Mixonomata, trhypochthoniid Desmonomata), nor in astigmatid mites.This revised version was published online in May 2005 with a corrected cover date.     

Chemical communication in the lacertid lizard Podarcis muralis: the functional significance of testosterone

Chemical signals are essential for intersexual communication in many animals, including lizards. While faeces have been suggested to contain socially relevant chemical stimuli, epidermal gland secretions are generally believed to be the leading source of chemosignals involved in lizard communication. Early research has shown that sex hormones affect epidermal gland activity, with androgens stimulating gland/pore size and/or gland productivity. However, the functional significance of hormone‐induced glandular activity in lizard chemical communication remains unclear. In this study, we manipulated testosterone (T) concentrations in male Podarcis muralis lizards. While T‐supplementation did not change pore size, it did increase secretion production substantially. Chemosensory tests showed that female conspecifics tongue‐flick at a higher rate and more quickly towards the secretion of males with experimentally increased T levels than towards the secretion of control males, suggesting that females can discriminate between males with dissimilar T levels based on chemical cues of secretion alone. Based on the scent of faeces, however, females were unable to discriminate between males with differential T levels. Also, females reacted more quickly when offered larger amounts of secretion – irrespective of whether secretions were obtained from control or T‐increased males. This result indicates that secretion quantity affects chemosignal detectability in Podarcis muralis.     

Innate and adaptive immune proteins in the preen gland secretions of male house sparrows

Recent studies have demonstrated that preen oil acts to reduce or eliminate feather-associated bacteria. The mechanisms underlying this antibacterial activity, however, are incompletely understood. In addition to the activity of alcohols (i.e. 3,7-dimethyloctan-1-ol), recent research has suggested that antimicrobial peptides may underlie the antibacterial activity of preen oil. Here, we document the presence of innate and adaptive immune proteins, lysozyme and immunoglobulin Y (IgY), in the preen oil of house sparrows Passer domesticus. We suggest lysozyme functions as an antimicrobial agent, with potentially important impacts against Gram-positive feather degrading bacteria. Furthermore, both lysozyme and IgY likely act in local immune defence of the preen gland, and may also play a role in regulating the local microbiome, with potentially important consequences for chemical communication and signalling. Our findings suggest that the preen gland and its secretions should be considered an integral part of the body's first line of defence against invading infections.     

Attraction of Culex pipiens to uropygial gland secretions does not explain feeding preference for American robins

Culex pipiens, the endemic mosquito vector of West Nile virus in eastern North America, is responsible for maintenance of the virus in avian reservoir hosts, the most important of which appears to be the American robin. One reason for the greater involvement of robins is believed to be the feeding preference of Cx. pipiens, however, the basis of this preference is not understood. We tested the hypothesis that the species‐specific chemical profile of avian uropygial gland secretions are used by Cx. pipiens as cues to locate birds and, therefore, may contribute to the observed feeding preferences. We used gas chromatography‐mass spectrometry to identify the semi‐volatile components of the uropygial gland secretions of American robins and two other common reservoir host species, the house sparrow and European starling. We found that the chemical composition of the robin secretions was different from those of the sparrows and starlings. Through behavioral choice trials conducted in a dual‐port olfactometer, we also found that Cx. pipiens did not prefer the secretions of robins over the other two species. Surprisingly, however, we found that Cx pipiens were more often attracted to live starlings over robins and to the secretions of starlings over those of robins.     

Non‐trophic effects of oribatid mites on cord‐forming basidiomycetes in soil microcosms

1. Saprotrophic cord‐forming basidiomycetes are the primary agents of decomposition in forest ecosystems. Collembola and oribatid mites affect fungal growth and foraging, and therefore decomposition, through direct mycelial grazing. 2. Grazing on the fungal species Hypholoma fasciculare, Resinicium bicolor and Phanerochaete velutina by the collembola Folsomia candida, and the oribatid mites Steganacarus magnus, Euzetes globulus and Hermannia gibba was investigated in soil microcosms. 3. Folsomia candida grazed on all fungal species: radial extent of R. bicolor, hyphal coverage of all fungal species, and fractal dimension of R. bicolor and P. velutina were all reduced. Oribatid mites did not graze the fungi but did affect mycelial morphology. Steganacarus magnus caused a reduction in the radial extent of H. fasciculare, and the hyphal coverage and fractal dimension in both H. fasciculare and R. bicolor. Euzetes globulus and H. gibba reduced the hyphal coverage of P. velutina. 4. Oribatid mites are associated with a cornucopia of chemical secretions with possible anti‐fungal properties. Chemical analysis of H. gibba opisthonotal secretions revealed four main compounds, all of which are new to the known spectrum of opisthonotal components. The most abundant was (E)‐β‐farnesene. 5. Treatment effects were species‐specific in terms of both fungal and invertebrate species. This study provides the first evidence of non‐grazing effects of oribatid mites on fungal growth and morphology. This could potentially influence the spatial organisation of mycelium in forest soils and therefore the ability of fungi to locate, colonise and decompose dead organic matter.     

Effect of Heliothis subflexa herbivory on fruit abscission by Physalis species: the roles of mechanical damage and chemical factors

1. Insect oral secretions are important for the induction of a number of plant responses, but the relative role of mechanical damage in the induction of these responses is often not well understood. Damage from the frugivore Heliothis subflexa, a specialist on Physalis species, causes herbivore‐induced fruit abscission. In this field study, we examined the separate and combined effects of mechanical damage and H. subflexa oral secretions on Physalis fruit abscission. 2. To determine the relative role of mechanical and chemical factors, the following treatments were administered to fruit: (1) three levels of mechanical damage, (2) natural herbivore damage by control larvae and by larvae surgically treated to inhibit saliva secretion, and (3) injection of H.subflexa oral secretions and a water control. Abscission of mechanically damaged fruit with and without the addition of oral secretions was also compared. 3. Mechanical damage was sufficient to cause fruit abscission, and the addition of oral secretions to mechanically damaged fruit did not cause an increase in fruit abscission. Normal caterpillars and those treated to inhibit saliva secretion caused similar abscission rates. 4. Though most studies examining the effects of insect oral secretions on induced plant responses find these chemical stimuli to be important or essential, the results of the present study showed that oral secretions are not necessary for fruit abscission. Future work is needed to determine the relative importance of mechanical damage in herbivore‐induced plant responses in other systems.     

Seasonal, sexual and developmental differences in hoopoe Upupa epops preen gland morphology and secretions: evidence for a role of bacteria

The uropygial glands of birds serve multiple functions, and there is great interspecific variability in the composition and properties of their secretions. A special case is the secretion in the hoopoes Upupa epops, and green woodhoopoes Phoeniculus purpureus, which, contrary to the commonly white and odourless secretions, are dark with pungent odour. Recently, bacteria have been isolated from glands of both woodhoopoes and hoopoes and here we test the hypothesis that bacteria are responsible of some of the special properties of glands and secretions of this group of birds. We explore natural seasonal changes and intersexual differences in the properties of hoopoe glands and secretions, check the natural occurrence of bacteria within secretions, and analyse the effect of experimental injection of antibiotics on uropygial gland properties. Male glands underwent no seasonal changes, and their secretions were invariably white and odourless, very similar to female glands outside the breeding season. However, in comparison to the uropygial gland of non‐breeding females, those of incubating females showed a marked increase in size and volume of secretion produced, which became dark and pungent. All these parameters increased until the hatching date and returned to values similar to those in the prelaying phase towards the end of the nestling period. Nestling glands produced secretions similar to those of females in colour and odour. Gland size of both females and nestlings predicted the amount of secretion produced. Microscopic techniques confirmed the presence of bacteria at high density and in active division in all dark secretions examined. The antibiotic treatment significantly reduced the load of enterococci in nestling glands, did not affect size of glands, but diminished the volume of secretion, which was lighter in colour than that of control nestlings. In nesting females, the experimental injection of antibiotic affected some measurements of gland size and secretion colour. Because the experiment did not affect general health estimates (immunocompetence, body condition or growing) of nestlings, our results suggest that some of the special properties of hoopoe glands are mediated by the presence of symbiotic bacteria.     

Coordination of Raiding and Emigration in the Ponerine Army Ant Leptogenys distinguenda (Hymenoptera: Formicidae: Ponerinae): A Signal Analysis

Several glandular sources of trail pheromones have been discovered in army ants in general. Nevertheless, at present the understanding of the highly coordinated behavior of these ants is far from complete. The importance of trail pheromone communication for the coordination of raids and emigrations in the ponerine army ant Leptogenys distinguenda was examined, and its ecological function is discussed. The secretions of at least two glands organize the swarming activities of L. distinguenda. The pygidial gland is the source of an orientation pheromone holding the group of raiding workers together. The same pheromone guides emigrations to new nest sites. In addition, the poison sac contains two further components: one with a weak orientation effect and another which produces strong, but short-term attraction and excitement. The latter component is important in prey recruitment and characterizes raid trails. This highly volatile recruitment pheromone allows the extreme swarm dynamic characteristic of this species. Emigration trails lack the poison gland secretion. Due to their different chemical compositions, the ants are thus able to distinguish between raid and emigration trails. Nest emigration is not induced chemically, but mechanically, by the jerking movements of stimulating workers.     

Local–regional boundary shifts in oribatid mite (Acari: Oribatida) communities: species–area relationships in arboreal habitat islands of a coastal temperate rain forest, Vancouver Island, Canada

Aim This study investigates the species–area relationship (SAR) for oribatid mite communities of isolated suspended soil habitats, and compares the shape and slope of the SAR with a nested data set collected over three spatial scales (core, patch and tree level). We investigate whether scale dependence is exhibited in the nested sampling design, use multivariate regression models to elucidate factors affecting richness and abundance patterns, and ask whether the community composition of oribatid mites changes in suspended soil patches of different sizes. Location Walbran Valley, Vancouver Island, Canada. Methods A total of 216 core samples were collected from 72 small, medium and large isolated suspended soil habitats in six western redcedar trees in June 2005. The relationship between oribatid species richness and habitat volume was modelled for suspended soil habitat isolates (type 3) and a nested sampling design (type 1) over multiple spatial scales. Nonlinear estimation parameterized linear, power and Weibull function regression models for both SAR designs, and these were assessed for best fit using R² and Akaike's information criteria (ΔAIC) values. Factors affecting oribatid mite species richness and standardized abundance (number per g dry weight) were analysed by anova and linear regression models. Results Sixty‐seven species of oribatid mites were identified from 9064 adult specimens. Surface area and moisture content of suspended soils contributed to the variation in species richness, while overall oribatid mite abundance was explained by moisture and depth. A power‐law function best described the isolate SAR (S = 3.97 × A^0.12, R² = 0.247, F_1,70 = 22.450, P < 0.001), although linear and Weibull functions were also valid models. Oribatid mite species richness in nested samples closely fitted a power‐law model (S = 1.96 × A^0.39, R² = 0.854, F_1,18 = 2693.6, P < 0.001). The nested SAR constructed over spatial scales of core, patch and tree levels proved to be scale‐independent. Main conclusions Unique microhabitats provided by well developed suspended soil accumulations are a habitat template responsible for the diversity of canopy oribatid mites. Species–area relationships of isolate vs. nested species richness data differed in the rate of accumulation of species with increased area. We suggest that colonization history, stability of suspended soil environments, and structural habitat complexity at local and regional scales are major determinants of arboreal oribatid mite species richness.     

The Releaser Effects of the Tergal Gland Secretion of Queen Honeybees (Apis mellifera)

Queen honeybees are attractive to their workers, due partially to the pheromonal bouquet they secrete. Queen mandibular gland pheromone is a powerful attractant to worker honeybees but it is not solely responsible for eliciting retinue behavior. The attractiveness of virgin queen tergal gland secretions and queen mandibular pheromone to worker honeybees was tested using a retinue bioassay. The number of workers attending the treated pseudoqueen lures was videorecorded in order to allow for the quantification of attractiveness. Queen mandibular gland secretions were more attractive than tergal gland secretions (P 0.008), and both queen tergal gland secretions (P 0.0002) and mandibular gland secretions (P 0.0001) were significantly more attractive than the control treatment. This laboratory bioassay indicates that queen tergal gland secretions have a releaser effect that evokes retinue behavior from worker honeybees.     

From preen secretions to plumage: the chemical trajectory of blue petrels' Halobaena caerulea social scent

Petrel seabirds heavily rely on their olfactory sense and are thus appropriate models for the study of avian chemical communication. The uropygial secretions of blue petrels Halobaena caerulea, for instance, have been shown to encapsulate elaborate sociochemical information including species, gender and identity. Yet, it is the plumage, and not preening secretions per se, which acts as the final substrate of avian scents. Importantly, the chemical relationship between secretions from the uropygial gland, located at the dorsal base of the tail, and plumage lipids has been considered in only a handful of studies which reported large qualitative differences. The emission process of avian scents, and the possible participation of the uropygial gland in particular, are therefore not elucidated. In the present study, we examine the early chemical trajectory of blue petrels' social chemosignals by comparing secretion and feather samples using Gas‐Chromatography Mass‐Spectrometry (GC/MS) and recently developed multivariate statistics. Our results indicate that (1) 85% of the feather lipids come from the uropygial secretions, (2) chemical differentiation between secretions and feather lipids includes qualitative and quantitative variations, which both have interesting implications for scent production, (3) the sociochemical information contained within the secretions (i.e. a sex‐specific signal and individual chemical signatures) are present in very conserved forms on the plumage. In the light of these results, it is apparent that the uropygial gland plays a critical role for chemical communication in petrels and possibly other avian groups.     

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.     

Ant–hemipteran association decreases parasitism of Phenacoccus solenopsis by endoparasitoid Aenasius bambawalei

1. Mutualism between ants and honeydew-excreting hemipterans is ubiquitous in the ecosystem. It is widely accepted that ant tending facilitates the colony growth of hemipterans by protecting them from predators and parasitoids. However, few studies have explored how ant tending helps defend against natural enemies. 2. Ghost ant Tapinoma melanocephalum and the invasive mealybug Phenacoccus solenopsis have a close mutual relationship. Previous studies have shown that ghost ant tending can definitely reduce parasitism and visit frequency of Aenasius bambawalei, the dominant endoparasitoid of P. solenopsis. However, the ghost ant workers seldom attack the parasitoids. It is still unclear how the ghost ant adversely affects parasitoids. This study explored the mechanism underlying the impacts of ants on natural enemies of the mealybugs. 3. Honeydew produced by P. solenopsis was an attractant to A. bambawalei. Parasitoids exhibited less searching activity, shorter longevity and lower parasitism when supplied with less honeydew. Aenasius bambawalei showed significant avoidance of pygidial gland secretions and visual cues of ghost ants. Parasitism in plants treated with 6-methyl-5-hepten-2-one, actinidine, and gland extracts was significantly lower than that in plants treated only with solvents (paraffin oil or double-distilled water). 4. It is concluded that honeydew consumption by ghost ants could negatively influence the performance of parasitoids. The pygidial gland secretions and visual cues of ghost ants also significantly inhibit the parasitism. These results may contribute to a better understanding of the regulation mechanism in ant–hemipteran–enemy interactions.