Can venom volatiles be a taxonomic tool for Polistes wasps (Hymenoptera,Vespidae)?

In the present study, we investigated whether venom volatiles have a species-specific composition and could possibly be used to discriminate between related paper wasp species. We compared venom volatile chemical profiles, obtained through gas chromatography-mass spectrometry analyses, of three non-parasitic European Polistes species ( P. dominulus , P. gallicus and P. nimphus ). The results show that the venom volatile composition is indeed species specific and can thus be a useful systematic tool.     

Non-pollinator fig wasp impact on the reproductive success of an invasive fig tree: why so little?

Classical biological control agents fail to achieve an impact on their hosts for a variety of reasons and an understanding of why they fail can help shape decisions on subsequent releases. Ornamental Ficus microcarpa is a widely planted avenue fig tree that is invasive in countries where its pollinator (Eupristina verticillata) is also introduced. This tree also supports more than 20 species of non-pollinating fig wasps (NPFW) that feed in the figs and have the potential to reduce the plant’s reproduction. Odontofroggatia galili, one of the most widely introduced NPFW, has larvae that develop in galled ovules that might otherwise develop into seeds or support pollinator larvae. We examined the distribution and relative abundance of the pollinator and O. galili on F. microcarpa in China, towards the northern limit of the tree’s natural range, and in Italy where the two species have been introduced. Where they co-existed, we also recorded the impact of varying densities of O. galili on F. microcarpa seed and pollinator production. O. galili and E. verticillata displayed contrasting habitat preferences in China, with O. galili almost absent from warmer sites. O. galili abundance and sex ratios varied between the natural and introduced ranges. Figs with more O. galili contained fewer seeds and pollinator offspring, but reproduction was rarely inhibited totally. Additional species with a greater impact in the figs they occupy are needed if biocontrol of F. microcarpa is to be effective.     

Cooperation between non-relatives in a primitively eusocial paper wasp,Polistes dominula

In cooperatively breeding vertebrates, the existence of individuals that help to raise the offspring of non-relatives is well established, but unrelated helpers are less well known in the social insects. Eusocial insect groups overwhelmingly consist of close relatives, so populations where unrelated helpers are common are intriguing. Here, we focus on Polistes dominula—the best-studied primitively eusocial wasp, and a species in which nesting with non-relatives is not only present but frequent. We address two major questions: why individuals should choose to nest with non-relatives, and why such individuals participate in the costly rearing of unrelated offspring. Polistes dominula foundresses produce more offspring of their own as subordinates than when they nest independently, providing a potential explanation for co-founding by non-relatives. There is some evidence that unrelated subordinates tailor their behaviour towards direct fitness, while the role of recognition errors in generating unrelated co-foundresses is less clear. Remarkably, the remote but potentially highly rewarding chance of inheriting the dominant position appears to strongly influence behaviour, suggesting that primitively eusocial insects may have much more in common with their social vertebrate counterparts than has commonly been thought.     

Depreissia decipiens,an enigmatic canopy spider from Borneo revisited (Araneae,Salticidae), with remarks on the distribution and diversity of canopy spiders in Sabah,Borneo

Depreissia is a little known genus comprising two hymenopteran-mimicking species, one found in Central Africa and one in the north of Borneo. The male of Depreissia decipiens is redescribed, the female is described for the first time. The carapace is elongated, dorsally flattened and rhombus-shaped, the rear of the thorax laterally depressed and transformed, with a pair of deep pits; the pedicel is almost as long as the abdomen. The male palp is unusual, characterized by the transverse deeply split membranous tegulum separating a ventral part which bears a sclerotized tegular apophysis and a large dagger-like retrodirected median apophysis. The female epigyne consists of one pair of large adjacent spermathecae and very long copulatory ducts arising posteriorly and rising laterally alongside the spermathecae continuing in several vertical and horizontal coils over the anterior surface. Relationships within the Salticidae are discussed and an affinity with the Cocalodinae is suggested. Arguments are provided for a hypothesis that Depreissia decipiens is not ant-mimicking as was previously believed, but is a mimic of polistinine wasps. The species was found in the canopy in the Kinabalu area only, in primary and old secondary rainforest at 200–700 m.a.s.l. Overlap of canopy-dwelling spider species with those in the understorey are discussed and examples of species richness and endemism in the canopy are highlighted. Canopy fogging is a very efficient method of collecting for most arthropods. The canopy fauna adds an extra dimension to the known biodiversity of the tropical rainforest. In southeast Asia, canopy research has been neglected, inhibiting evaluation of comparative results of this canopy project with that from other regions. More use of fogging as a collecting method would greatly improve insight into the actual species richness and species distribution in general.     

An uneasy alliance:a nesting association between aggressive ants and equally fierce social wasps

Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder,its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta(F.).In French Guiana,83.33%of the 48 P.rejecta nests recorded were found side by side with those of A.chartifex.This nesting association results in mutual protection from predators(i.e.,the wasps protected from army ants;the ants protected from birds).We conducted field studies,laboratorybased behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association.Due to differences in the cuticular profiles of the two species,we eliminated the possibility of chemical mimicry.Also,analyses of the carton nests did not reveal traces of marking on the envelopes.Because ant forager flows were not perturbed by extracts from the wasps’Dufour’s and venom glands,we rejected any hypothetical action of repulsive chemicals.Nevertheless,we noted that the wasps"scraped"the surface of the upper part of their nest envelope using their mandibles,likely removing the ants'scent trails,and an experiment showed that ant foragers were perturbed by the removal of their scent trails.This leads us to use the term"erasure hypothesis."Thus,this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to"contain"their associated ants through the elimination of their scent trails,direct attacks,"wing-buzzing"behavior and ejecting the ants.     

Beyond the wasp‐waist: structural diversity and phylogenetic significance of the mesosoma in apocritan wasps (Insecta: Hymenoptera)

A comprehensive data set of hymenopteran mesosomal anatomy is presented and analysed. Eighty‐nine taxa, including three outgroups, were scored for 273 characters. Analyses were carried out under different weighting conditions (equal and implied weights). Topologies retrieved for the non‐apocritan Hymenoptera were highly congruent with previously published results. Apocrita were always retrieved as monophyletic, as were most superfamilies. Relationships amongst apocritan superfamilies were mostly weakly corroborated. Stephanoidea were almost always the sister group to the remaining Apocrita. Evaniomorpha were usually retrieved, Ceraphronoidea being the sister group to Megalyroidea, and Evanioidea to Trigonaloidea. Aculeata did not always come out as monophyletic, and of the aculeate superfamilies, only Apoidea was retrieved. Ichneumonoidea were always monophyletic and often the sister group of Aculeata. Maamingidae and Mymarommatoidea were usually sister groups; together, they often form the sister group of Chalcidoidea. A large clade comprising Cynipoidea, Platygastroidea, and Proctotrupoidea was usually retrieved, the two former superfamilies being nested within Proctotrupoidea. Cynipoidea were usually closely related to some of the Diapriidae. Platygastroidea were usually the sister group of a clade comprising Heloridae, Pelecinidae, Proctotrupidae, and Vanhorniidae. The mesosomal region proved to be a very substantial source of phylogenetically relevant information. The results of the present analyses indicate that a reclassification, especially of Proctotrupoidea, is required, but this should be carried out after thorough analyses of more comprehensive combined data sets. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 22–194.     

Behaviour of pollinator insects within inflorescences of Scrophularia species from Iberian Peninsula

Several hypotheses have been proposed to explain the pattern of pollinator visits to vertical inflorescences. These range from a response to a pattern of resources to merely instinctive behaviour. In dichogamous plants, such behaviour has been associated with promoting outcrossing and avoiding geitonogamy. We here analyse behaviour of the principal pollinator groups in five protogynous species of Scrophularia with different flower sizes (S. sambucifolia, S. grandiflora, S. lyrata, S. scorodonia and S. canina), and the distribution of sexual phases along the inflorescences. The results in all cases show that pollinators follow a pattern of ascending visits accompanied by movements between flowers of the same whorl (horizontal movements). The relative frequency of these horizontal movements depends on the flower size, with a higher frequency in species with large flowers. In vertical movements of the three more common pollinator groups to several plant species (bumblebees, wasps and small bees), the behaviour was essentially independent of flower size, with bumblebees having the highest ratio of ascents to descents. Behaviour of the pollinators, together with the absence of a definite pattern of distribution of the sexual phases along the inflorescence, implies that geitonogamy is not avoided in any of the Scrophularia species studied.     

Fungal endophytes which invade insect galls: insect pathogens,benign saprophytes,or fungal inquilines?

Fungi are frequently found within insect galls. However, the origin of these fungi, whether they are acting as pathogens, saprophytes invading already dead galls, or fungal inquilines which invade the gall but kill the gall maker by indirect means, is rarely investigated. A pathogenic role for these fungi is usually inferred but never tested. I chose the following leaf-galling-insect/host-plant pairs (1) a cynipid which forms two-chambered galls on the veins of Oregon white oak, (2) a cynipid which forms single-chambered galls on California coast live oak, and (3) an aphid which forms galls on narrowleaf cottonwood leaves. All pairs were reported to have fungi associated with dead insects inside the gall. These fungi were cultured and identified. For the two cynipids, all fungi found inside the galls were also present in the leaves as fungal endophytes. The cottonwood leaves examined did not harbor fungal endophytes. For the cynipid on Oregon white oak, the fungal endophyte grows from the leaf into the gall and infects all gall tissue but does not directly kill the gall maker. The insect dies as a result of the gall tissue dying from fungal infection. Therefore, the fungus acts as an inquiline. Approximately 12.5% of these galls die as a result of invasion by the fungal endophyte.     

Functional principles of steerable multi‐element probes in insects

Hemipterans, mosquitoes, and parasitic wasps probe in a variety of substrates to find hosts for their larvae or food sources. Probes capable of sensing and precise steering enable insects to navigate through solid substrates without visual information and to reach targets that are hidden deep inside the substrate. The probes belong to non‐related taxa and originate from abdominal structures (wasps) or mouthparts (hemipterans and mosquitoes), but nevertheless share several morphological characteristics. Although the transport function clearly differs (egg laying and acquisition of liquid food), the functional demands on the mechanical behaviour of the probe within the substrate tend to be similar. The probe needs to be thin to limit substrate deformation, and long, in order to attain substantial path lengths or depths. We linked the morphology across taxa to the different functional requirements, to provide insights into the biology of probing insects and the evolution of their probes. Current knowledge of insect probes is spread over many taxa, which offers the possibility to derive general characteristics of insect probing. Buckling during initial puncturing is limited by external support mechanisms. The probe itself consist of multiple (3–6) parts capable of sliding along one another. This multi‐part construction presumably enables advancement and precise three‐dimensional steering of the probe through the substrate with very low net external pushing forces, preventing buckling during substrate penetration. From a mechanical viewpoint, a minimum of three elements is required for 3D steering and volumetric exploration, as realised in the ovipositors of wasps. More elements, such as in six‐element probes of mosquitoes, may enhance friction in soft substrates. Alternatively, additional elements can have functions other than ‘drilling’, such as saliva injection in mosquitoes. Despite the gross similarities, probes show differences in their cross sections, tip morphologies, relative lengths of their elements, and the shape of their interconnections. The hypothesis is that the probe morphology is influenced by the substrate properties, which are mostly unknown. Correlating the observed diversity to substrate‐specific functional demands is therefore currently impossible. We conclude that a multipart probe with sliding elements is highly effective for volumetric substrate probing. Shared functional demands have led to an evolutionary convergence of slender multi‐element probes in disparate insect taxa. To fully understand 3D probing, it is necessary to study the sensory and material properties, as well as the detailed kinematics and dynamics of the various probes in relation to the nature of the selective pressure originating from the species‐specific substrates. Such knowledge will deepen our understanding of probing mechanisms and may support the development of slender, bio‐inspired probes.     

Asymmetric Assortative Mating Behaviour Reflects Incomplete Pre‐zygotic Isolation in the Nasonia Species Complex

Preference of con‐ over heterospecific mates leading to assortative mating can substantially contribute to pre‐zygotic reproductive isolation and prevent fitness losses if post‐zygotic hybridization barriers already exist. The jewel wasp genus Nasonia displays quite strong and well‐studied post‐zygotic reproductive isolation due to a ubiquitous Wolbachia infection causing cytoplasmic incompatibility between different species. Pre‐zygotic isolation, however, has received far less research attention in this model organism, especially concerning the mechanisms and criteria of mate choice. In the present study, we analysed mate rejection and mate acceptance rates in cross‐comparisons between all four Nasonia species. We put emphasis on observing which sex is more likely to interrupt interspecific matings and how discriminatory behaviour varies across the different species in all possible combinations. We found an asymmetric distribution of assortative mating among the four Nasonia species that appears to be highly influenced by the respective combinations of sex and species. Females appeared to be the main discriminators against heterospecific mating partners, but interestingly, we could also detect mate discrimination and rejection behaviour in males, a widely neglected factor in research on mating behaviour in general and on Nasonia in particular. Moreover, the asymmetry in the assortative mating behaviour was partially reflective of sym‐ or allopatric distributions of natural Nasonia populations.