Testing the selectiveness of electric harps: a mitigation method for reducing Asian hornet impact at beehives.

The Asian hornet (Vespa velutina) has rapidly become a source of stress for the beekeeping sector. Several methods have been developed to control its impact and spread, though some of these impose a high risk for native insects. Among these methods are electric harps, which are physical barriers that electrocute hornets passing through two wires powered by a current generator. However, the risk to local fauna of electric harps has not previously been tested. Here we evaluated the selectiveness and risk of damage for local entomofauna of the electric harps in a study carried out over three years and four locations in Girona province (NE Catalonia, Spain). The electric harps showed a high selectiveness, with 82.9% of all insects trapped (3,902 individuals) catalogued as Asian hornets, although this greatly varied over years and locations with values ranging from 20.5% to 94.3%. The risk damage of electric harps for local entomofauna was very low in all surveyed areas and years. Native insects accounted for, as a mean, 1.7% of all insects trapped over the study period (range 0-4.5%). Accordingly, the electric harps imply a low risk for the native European hornet Vespa crabro, since only 0.1% of the captures belonged to that species. Our results suggest that electric harps might be a useful method to reduce predation pressure of the Asian hornet at beehives while imposing a low risk for local entomofauna. The employment of standardised techniques, such as the placement of electric harps, may be useful to assess inter-annual variations or site-specific differences on the predation pressure of the Asian hornet at beehives. Further research should evaluate whether the placement of electric harps improves bee colony survival or vigour parameters (i.e. honey production, amount of brood, pollen, etc.).

Interspecific variation of antennal lobe composition among four hornet species

Olfaction is a crucial sensory modality underlying foraging, social and mating behaviors in many insects. Since the olfactory system is at the interface between the animal and its environment, it receives strong evolutionary pressures that promote neuronal adaptations and phenotypic variations across species. Hornets are large eusocial predatory wasps with a highly developed olfactory system, critical for foraging and intra-specific communication. In their natural range, hornet species display contrasting ecologies and olfactory-based behaviors, which might match to adaptive shifts in their olfactory system. The first olfactory processing center of the insect brain, the antennal lobe, is made of morphological and functional units called glomeruli. Using fluorescent staining, confocal microscopy and 3D reconstructions, we compared antennal lobe structure, glomerular numbers and volumes in four hornet species (Vespa crabro, Vespa velutina, Vespa mandarinia and Vespa orientalis) with marked differences in nesting site preferences and predatory behaviors. Despite a conserved organization of their antennal lobe compartments, glomeruli numbers varied strongly between species, including in a subsystem thought to process intraspecific cuticular signals. Moreover, specific adaptations involving enlarged glomeruli appeared in two species, V. crabro and V. mandarinia, but not in the others. We discuss the possible function of these adaptations based on species-specific behavioral differences.

Identification of pathogens in the invasive hornet Vespa velutina and in native Hymenoptera (Apidae, Vespidae) from SW-Europe

Invasive species contribute to deteriorate the health of ecosystems due to their direct effects on native fauna and the local parasite-host dynamics. We studied the potential impact of the invasive hornet Vespa velutina on the European parasite-host system by comparing the patterns of diversity and abundance of pathogens (i.e. Microsporidia: Nosematidae; Euglenozoa: Trypanosomatidae and Apicomplexa: Lipotrophidae) in European V. velutina specimens with those in the native European hornet Vespa crabro, as well as other common Hymenoptera (genera Vespula, Polistes and Bombus). We show that (i) V. velutina harbours most common hymenopteran enteropathogens as well as several new parasitic taxa. (ii) Parasite diversity in V. velutina is most similar to that of V. crabro. (iii) No unambiguous evidence of pathogen release by V. velutina was detected. This evidence together with the extraordinary population densities that V. velutina reaches in Europe (around of 100,000 individuals per km2 per year), mean that this invasive species could severely alter the native pathogen-host dynamics either by actively contributing to the dispersal of the parasites and/or by directly interacting with them, which could have unexpected long-term harmful consequences on the native entomofauna.

Different trophic positions among social vespid species revealed by stable isotopes

The social vespid wasps are common insect predators and several species behave in unison in the same biotopes. It is commonly accepted that social wasps are mainly opportunistic generalist predators without differences in prey selection and hence they compete for the same food resources. Trophic positions of six vespid wasp species and their potential prey from four sites in Finland and one in the UK were evaluated using carbon and nitrogen stable isotopes (δ 13 C and δ 15 N). The difference in isotope values indicated different trophic positions among species. In general, Dolichovespula spp. showed higher δ 15 N values than Vespula spp., which suggests that Dolichovespula forage on higher trophic levels. Dolichovespula media (Retzius, 1783) showed the highest δ 15 N values, whereas Vespula vulgaris showed the lowest. Dolichovespula media partly expresses apex predator-like δ 15 N values, whereas Vespula species tend to forage on primary consumers. The largest species Vespa crabro (Linnaeus, 1758) showed also similar δ 15 N values as Vespula spp. However, δ 13 C and δ 15 N values of V. vulgaris workers varied slightly during the season. This study offers novel insights about the trophic segregation in the social wasp community, suggesting specialization in diet resource utilization, especially between Dolichovespula and Vespula .

First Discovery of Vespa velutina nigrithorax du Buysson (Hymenoptera: Vespidae), an Invasive Hornet in the Feces of the Yellow-Throated Marten in South Korea

Yellow-throated martens (YTMs) are omnivores that often prey on wasps in late autumn in Korea. However, to the best of our knowledge, predation of the invasive alien species Vespa velutina nigrithorax (VVN) has not previously been investigated. In this study, YTM feces were collected and analyzed from Mt. Onggangsan, Sinwon-ri, Cheongdo, South Korea, where VVN density was high and YTMs were active. Surveys were conducted three times between October and December 2019, during which a total of 22 samples were collected. Debris from VVN was found in three samples, along with evidence of two indigenous wasps, Vespa crabro and Vespula koreensis. The VVN remains were identified as one queen, four males, one female, and one individual whose caste was unclear. Martens prey on wasps, owing to a sudden decrease in plant food sources from late autumn to early winter, mostly eating males and new queens attempting to mate. If VVN reproduction is prevented or disturbed by YTM predation, there may be potential biological control effects in areas with high VVN density. Further studies should be conducted to verify whether there is a practical biological control effect.

Essential (Mg, Fe, Zn and Cu) and Non-Essential (Cd and Pb) Elements in Predatory Insects (Vespa crabro and Vespa velutina): A Molecular Perspective

The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies.

Introduced Vespa velutina does not replace native Vespa crabro and Vespula species

Alien species invasion could lead to the replacement of native species with similar ecological requirements. Vespa velutina is an invasive hornet recently established in Europe, that is raising concern due to the associated economic and ecological impacts toward managed and wild pollinators besides to the potential competition and replacement of native wasp species. This led to the inclusion of V. velutina in the European list of Invasive Alien Species of Union concern. Nevertheless, V. velutina impacts on the native wasp community is poorly understood. We analysed the influence of V. velutina abundance on the European hornet Vespa crabro in a four-year invaded area in Italy. Moreover, we assessed the impacts of its presence on V. crabro, Vespula vulgaris and Vespula germanica, by comparing the invaded area with an uninvaded one. A Bayesian Generalized Linear Model, implemented to control some relevant environmental confounders, indicate that the relationship between Vespa species was positive at low abundances, while for high values of V. velutina the two species did not covary anymore. The distribution of V. crabro, V. vulgaris and V. germanica showed a considerable overlap between the invaded and uninvaded areas. Overall, the results bring to the conclusion that native Vespidae have probably avoided or minimised a competition pressure, and therefore the presence of V. velutina has not led to an evident replacement of V. crabro and Vespula species. This provides reassurance regarding the conservation status of native European Vespidae following V. velutina invasion.