Adverse effects of the fungal biopesticide Beauveria bassiana on a predatory social wasp

Biopesticides are considered eco-friendly alternatives to synthetic agrochemicals. However, their impact on non-target organisms is still poorly understood. Social wasps, in particular, are a largely neglected group when it comes to risk assessment of plant protection products, despite the relevant ecological and economic services provided by these insects. In the present study, we evaluated the impact of a common biopesticide, the entomopathogenic fungus Beauveria bassiana, on the paper wasp Polistes dominula. We adopted a holistic approach in ecotoxicology by focusing not only on the detrimental effects on isolated individuals, but also on the whole colony. Both adult wasps belonging to different castes and immature larvae were topically exposed to a field-realistic concentration of fungal spores from the commercial strain of B. bassiana ATCC 74040 to assess the impact of the biopesticide on their survival, behavior and physiology. Our results showed that the fungus causes a number of adverse effects on P. dominula, that include increased mortality, altered locomotion and feeding rate, selective ejection of exposed larvae from nests, reduced oviposition rate and ovary development in foundresses, and colony failure. Our findings provide new insights on the often-neglected sublethal effects of pollutants that can jeopardize not only individual beneficial insects, but also the delicate social balance of their colonies and their valuable ecosystem services, highlighting that the natural origin of plant-protection products does not always guarantee environmental safety.

Histology and ultrastructure of glands associated with the sting apparatus of the swarm-founding wasp Protopolybia exigua (Hymenoptera: Vespidae: Polistinae)

Social insects present a great diversity of exocrine glands, which are linked to fundamental roles of social life, and their morphological characterization represents the first step toward the knowledge of their function. We here describe the exocrine glands present in the sting apparatus of queens and workers of the wasp Protopolybia exigua. Histological analysis of serial sections under light microscopy revealed a glandular epithelium in the spiracular plate, the quadrate plate, and the gonostyli, while the last two in addition also contain clusters of class-3 cells. A big cluster of class-3 cells was also found in the oblong plate of some workers and queens. These findings reveal that a variety of glands, in addition to the common venom gland and Dufour gland, are present in association with the sting apparatus, of which three glands are novel reports for the exocrine repertoire of social insects. The position of the glands suggests a role in lubrication to provide mobility of the sting and venom ejection and/or participation in alarm behavior, while a function related to reproduction is also possible. The peculiar characteristics displayed by swarm-founding wasps are linked with exocrine gland secretions, making their investigation in Epiponini wasps a vast and interesting field.

Honeybee queen mandibular pheromone fails to regulate ovary activation in the common wasp

The queen mandibular pheromone (QMP) identified from the honeybee is responsible for maintaining reproductive division of labour in the colony, and affects multiple behaviours. Interestingly, QMP inhibits reproduction not only in honeybee workers, but also in distantly related insect species such as fruit flies and bumblebees. This study examines whether QMP also affects worker reproduction in the common wasp Vespula vulgaris. Wasp workers were exposed to one of the following treatments: QMP, wasp queen pheromone (the hydrocarbon heptacosane n-C₂₇), or acetone (solvent-only control). After dissecting the workers, no evidence that QMP inhibits development in V. vulgaris could be found. However, this study could confirm the inhibitory effect of the hydrocarbon heptacosane on ovary activation. The reason why non-social species such as the fruit fly and social species such as bumblebees and ants respond to the QMP, while the social wasp V. vulgaris does not, is unclear. The investigation of whether olfaction is key to sensing QMP in other insect species, and the detailed study of odorant receptors in other social insects, may provide insights into the mechanisms of response to this pheromone.

Camouflaged Nests of Mischocyttarus mirificus (Hymenoptera, Vespidae)

Social wasps present various architectural patterns for their nests, which may differ in shape, size, color, and material used in construction. The distribution pattern of comb cells presented by Mischocyttarus mirificus (Zikán, 1935) is vertical with a single cell of width, resulting in a filiform shape that camouflages in the middle of the substrate. There are few studies regarding this architectural pattern for social wasps and their role in camouflage, and this study aims to detail the nesting habits of this species. In total, 40 colonies were analyzed in their natural habitat and six were dissected in the laboratory. Aspects about the construction of the nests and nesting environment have been described. A test was carried out with nest photographs, to quantify their camouflage percentage within the nesting substrate. The colonies were found mainly in riparian forests where there were elements in the environment that favored their camouflage. According to the nest photograph analysis, their camouflage levels can vary according to the position from which the photograph is taken. It is evident that M. mirificus founders select sites where they can camouflage their colonies, and this gives them advantages in exploring a new environment.

N-(3-methylbutyl)butanamide: A novel amide in the venom of female social wasps, Vespula vulgaris

In New Zealand's ancient Fuscospora spp. or beech forests, two invasive Vespula social wasps Vespula vulgaris (L.) and Vespula germanica (F.) have become significant problems, adversely affecting native birds and invertebrate biodiversity. The nature of chemical communication in these two species is poorly understood, and this work was undertaken to identify the behaviourally active compounds in the venom of the common wasp, Vespula vulgaris (L.). Venom was removed from the stings of both workers and females and analyzed by coupled gas chromatography/electroantennographic detection (GC/EAD) and gas chromatography/mass spectrometry (GC/MS). Two compounds were present in the venom that consistently elicited EAD responses from the antennae of males and workers. Mass spectrometry analysis and syntheses of candidate structures revealed the structures to be N-(3-methylbutyl)acetamide (MBA) and N-(3-methylbutyl)butanamide (MBB). Gyne venom contains significantly larger amounts of MBA and MBB than worker venom. When these two compounds were tested in the field individually or as binary blends in combination with the known food odour (honeydew volatiles), only N-(3-methylbutyl)butanamide or blends containing this compound showed a strong repellent effect on workers to honeydew volatiles at all doses tested. This is the first report of the occurrence of N-(3-methylbutyl)butanamide in nature and the third amide to be identified in the venom of any social wasp. In addition, this work is the first to report the chemical analysis of the venom of V. vulgaris gyne. The repellency effect observed in this study of the venom compound suggests that our definition and understanding of the function of the alarm pheromone need to be reassessed.

Spatial memory in Vespula germanica wasps: A pilot study using a Y-maze assay

In the present study we analysed spatial learning in Vespula germanica wasps when dealing with a walking Y-maze. We recorded the time taken to leave the maze during two consecutive visits and which of the two short arms was chosen to exit. Two treatments were conducted to evaluate whether wasps learned to leave the Y-maze guided either by spatial or visual cues. In Treatment 1, the colour of both arms remained unchanged between two consecutive visits; and in Treatment 2, the position of the coloured arm was switched after the first trial. Our results demonstrated that the time taken to exit the maze on the second trial was less than half in both treatments and wasps left the maze from the previously chosen arm, irrespective of its colour. This is the first study to demonstrate spatial learning in V. germanica wasps by using a walking Y-maze. Free flying wasps learned to enter the Y-maze on their own volition, walk through it, collect food and find their way out more rapidly after a single foraging experience. The current experimental device is suitable for the evaluation of spatial memory processes and exploratory behaviour in this species.

First Record of a B Chromosome in Polybia fastidiosuscula Saussure (Vespidae) and Investigation of Chromatin Composition Through Microsatellite Mapping

The characterization of karyotypes is an important aspect in understanding the structure and evolution of genomes. Polybia is a genus of social wasps of the family Vespidae. This genus has 58 species, but for only 8 of these chromosome number and morphology have been reported in the literature. The aim of this study was to describe and characterize the Polybia fastidiosuscula Saussure karyotype, presenting the first case of a B chromosome in Vespidae. In addition, we investigated the chromatin composition of this species through C-banding, base-specific fluorochrome staining, and physical mapping of 7 microsatellites and 18S rDNA. Four colonies of P. fastidiosuscula from Minas Gerais and Paraná states, Brazil, were analyzed. The chromosome number identified was 2n = 34, and 2 colonies presented a B chromosome. We characterized the chromatin composition of this species, analyzing the existence of different microsatellite-rich heterochromatic regions which are also enriched with AT or GC base pairs. We suggest an intraspecific origin of the B chromosome based on the homology of the heterochromatic composition with A chromosomes and also verify that the TTAGG and TCAGG sequences are not telomeric, but only microsatellites that occur in the centromeres of most chromosomes, as well as GAG and CGG.

Exocrine glands in the legs of the social wasp Vespula vulgaris

This study brings a survey of the exocrine glands in the legs of Vespula vulgaris wasps. We studied workers, males, virgin queens as well as mated queens. A variety of 17 glands is found in the different leg segments. Among these, five glands are novel exocrine structures for social insects (trochanter-femur gland, ventrodistal tibial gland, distal tibial sac gland, ventral tibial gland, and ventral tarsomere gland). Most leg glands are present in the three leg pairs of all castes. This may indicate a mechanical function. This is likely for the numerous glands that occur near the articulation between the various leg segments, where lubricant production may be expected. Other possible functions include antenna cleaning, acting as a hydraulic system, or pheromonal. Further research including leg-related behavioural observations and chemical analyses may help to clarify the functions of these glandular structures in the legs.

Facial markings in the social cuckoo wasp Polistes sulcifer: No support for the visual deception and the assessment hypotheses

Insect social parasites have to conquer a host colony by overcoming its defensive barriers. In addition to increased fighting abilities, many social parasites evolved sophisticated sensory deception mechanisms to elude host colonies defenses by exploiting host communication channels. Recently, it has been shown that the conspicuous facial markings of a paper wasp social parasite, Polistes sulcifer, decrease the aggressiveness of host foundresses. Two main hypotheses stand as explanations of this phenomenon: visual sensory deception (i.e. the black patterning reduces host aggression by exploiting the host visual communication system) and visual quality assessment (i.e. facial markings reduce aggressiveness as they signal the increased fighting ability of parasites). Through behavioral assays and morphological measurements we tested three predictions resulting from these hypotheses and found no support either for the visual sensory deception or for the quality assessment to explain the reduction in host aggressiveness towards the parasite. Our results suggest that other discrimination processes may explain the observed phenomenon.

Learning in an exotic social wasp while relocating a food source

In this paper we review several studies on Vespulagermanica behavioral plasticity while relocating a food source in natural environments. This exotic social wasp, which has become established in many parts of the world, displays diverse cognitive abilities when foraging. Given its successful invasiveness worldwide, our initial hypothesis was that this species has great behavioral plasticity, which enables it to face environmental uncertainty. In our work we have analyzed foraging behavior associated with undepleted resources. Throughout several experiments, rapid learning was observed in this species; after few learning experiences they associate diverse contextual cues with a food source. However, by exploring wasp behavior when food suddenly disappeared, either because it had been removed or displaced, we found that they continued searching over a no longer rewarding site for a considerable period of time, suggesting that past experience can hinder new learning. Particularly surprising is the fact that when food was displaced nearby, wasps persisted in searching over the empty dish, ignoring the presence of food close by. We propose that this species could be a suitable model for studying cognitive plasticity in relation to environmental uncertainty.