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Understanding the major mechanisms that allow an alien species to become invasive is crucial for limiting the impact of such species, and individual immunity seems to be a crucial trait for their large range colonization when introduced to a new area. Indeed, a high resistance to pathogens and parasites could favour the establishment and proliferation of an alien species in a newly colonized region. A striking example of recent successful invasion is represented by the Asian hornet, Vespa velutina nigrithorax, which has invaded Western Europe threatening bees and beekeeping activities. Investigating the biology of this species is fundamental to understand how V. velutina nigrithorax has become invasive in Europe and this knowledge could be crucial for limiting its impact. Here, by performing bacterial challenge bioassays, we compare the immune competence of different castes and sex of a population of the invasive Asian hornet, V. velutina nigrithorax, and of the native European hornet, V. crabro. Our results demonstrate that the two species differ in their immunocompetence with respect to caste: a higher level of immunocompetence was found in the reproductive females of the Asian hornet which were resistant to bacterial challenge when compared to workers and males of both species and to reproductive females of the native European hornet. The high pathogen resistance in reproductive females of the Asian hornet, might therefore represent a key factor contributing to the ecological success and spread of this invader. [ABSTRACT FROM AUTHOR]

Simple Summary: Hornets of the genus Vespa and honey bees are the main characters of a coevolutionary arms race that is made evident by the conspicuous number of reciprocal adaptations evolved by both predator and prey. Through this ancient process predatory hornets and honey bees seem to have reached a fragile balance, which is lost when alien hornet species are accidentally introduced into new geographic areas. This is the case of Asian hornet species, such as Vespa velutina and Vespa mandarinia, which have invaded Europe and North America in recent decades, with a heavy impact on Western honey bees and commercial beekeeping. Here, we provide a comprehensive review of the existing studies that have investigated the interactions between hornets and honey bees throughout the world, highlighting the complexity of the specialized strategies adopted by Asian honey bees and their sympatric predators and the relative lack of coevolution and effective defenses of Western honey bees against invasive hornets. Hornets and honey bees have a long history of coevolution resulting in a plethora of captivating adaptations and counteradaptations between predator and prey. From simple physiological mechanisms to complex behavioral strategies, some Vespa hornets have specialized in hunting honey bees, while the latter have put in place effective defenses to counteract their attack. Both hornets and honey bees have evolved the ability to detect the odors and the pheromones emitted by the other to locate the prey or to spot foraging predators. Hornets often rely on their bigger size, heavily armored body and destructive attacks, while honey bees differentiated collective defense responses finely coordinated to deter or kill the hornet menace. However, when new species of hornets and honey bees come into contact, the absence of coevolution can have a heavy impact on the defenseless bees. The evolutionary arms race between hornets and honey bees provides not only compelling examples of adaptations and counteradaptations between predator and prey, but could also represent a starting point for the development of effective and sustainable strategies to protect honey bees and beekeeping activities and to control invasive alien species of hornets. [ABSTRACT FROM AUTHOR]

Mimicry is one of the most fascinating phenomena in nature 1. Mimicry traits often reflect complex, finely tuned, and sometimes extravagant relationships among species and have evolved to deceive predators or prey. Indeed, mimicry has most often evolved to discourage predation: the 'mimic' exhibits phenotypic convergence towards a non-related 'model' organism which is inedible or harmful, so that a given predator, or 'receiver', will refrain from attacking or ingesting the mimic. Traditionally, mimicry is mainly evident and has been mainly studied in the visual domain. Here, we report experiments that document the first case of interspecific acoustic mimicry in a mammal and demonstrate that the distress calls the greater mouse-eared bat (Myotis myotis) broadcasts when handled imitate sounds of stinging bees or wasps to discourage the bat's avian predators. Ancillotto et al. report a case of interspecific acoustic mimicry in a mammal, and demonstrate that the distress calls of the greater mouse-eared bat imitate sounds of stinging social hymenopterans to discourage the bat's avian predators. [ABSTRACT FROM AUTHOR]