Olivier Bonnard

Vespa velutina: a new invasive predator of honeybees in Europe

The yellow-legged hornet (Vespa velutina) is the first invasive Vespidae predator of honeybees to be accidentally introduced into Europe from Asia. In the current pollinator decline, V. velutina is an additional stressor for honeybees and other pollinators. Although V. velutina contributes to the loss of honeybee colonies, little is known about its biology and behaviour both in the native and in the invaded area. Here, we review the current knowledge of this species and describe its life cycle and life history traits (reproduction, overwintering, foraging and dispersal) in the light of the biology of other Vespidae. We also review the impact of this species on ecosystems, on the economics of beekeeping, and on human health (this species being potentially deadly for allergic people). Based on this information and on previous worldwide experiences with Vespidae invasions, we propose key research topics for the development of effective management plans. We identify methods to limit the impact and proliferation of V. velutina in Europe that are based on nest destruction, trapping, population genetics, and biological control. In our opinion, research effort on the means to detect and destroy V. velutina nests at an early stage is required in order to short-circuit the colony cycle and thus limit both its impact on honeybees and its expansion through Europe. Finally, we discuss the impact of this biological invasion on the development of methods that should be used to manage alien species in the future.

Native Prey and Invasive Predator Patterns of Foraging Activity: The Case of the Yellow-Legged Hornet Predation at European Honeybee Hives

Contrary to native predators, which have co-evolved with their prey, alien predators often benefit from native prey naïveté. Vespa velutina, a honeybee predator originating from Eastern China, was introduced into France just before 2004. The present study, based on video recordings of two beehives at an early stage of the invasion process, intends to analyse the alien hornet hunting behaviour on the native prey, Apis mellifera, and to understand the interaction between the activity of the predator and the prey during the day and the season. Chasing hornets spent most of their time hovering facing the hive, to catch flying honeybees returning to the hive. The predation pressure increased during the season confirming previous study based on predator trapping. The number of honeybee captures showed a maximum peak for an intermediate number of V. velutina, unrelated to honeybee activity, suggesting the occurrence of competition between hornets. The number of honeybees caught increased during midday hours while the number of hornets did not vary, suggesting an increase in their efficacy. These results suggest that the impact of V. velutina on honeybees is limited by its own biology and behaviour and did not match the pattern of activity of its prey. Also, it could have been advantageous during the invasion, limiting resource depletion and thus favouring colonisation. This lack of synchronization may also be beneficial for honeybee colonies by giving them an opportunity to increase their activity when the hornets are less effective.

Defensive behaviour of Apis mellifera against Vespa velutina in France: Testing whether European honeybees can develop an effective collective defence against a new predator

We investigated the prey-predator interactions between the European honeybee, Apis mellifera, and the invasive yellow-legged hornet, Vespa velutina, which first invaded France in 2004 and thereafter spread to neighbouring European countries (Spain, Portugal and Italy). Our goal was to determine how successfully honeybees are able to defend their colonies against their new predator in Europe. Experiments were conducted in the southwest of France-the point of entry of the hornet in Europe-under natural and semi-controlled field conditions. We investigated a total of eight apiaries and 95 colonies subjected to either low or high levels of predation. We analyzed hornet predatory behaviour and collective response of colonies under attack. The results showed that A. mellifera in France exhibit an inefficient and unorganized defence against V. velutina, unlike in other regions of Europe and other areas around the globe where honeybees have co-evolved with their natural Vespa predators.

Behavioral syndrome in a native and an invasive hymenoptera species

Recent studies have focused on the role of behavior in biological invasions. Individuals may differ consistently in time for several behavioral traits (personality) which covary (behavioral syndrome) resulting in different behavioral types, some of them favoring invasion. Social hymenopterans have a strong potential to be invaders and their success depends primarily on the foundresses’ ability to found viable colonies. They are expected to be active, explorative and bold for optimally establishing their nest. In Europe, 2 hornet species coexist: the native Vespa crabro and the invasive Vespa velutina. These 2 species may compete for nesting sites and we suggest that the initial success of V. velutina has been favored by its behavior in outperforming V. crabro for the traits involved in nest initiation. Here, we (i) defined the personality of V. crabro and V. velutina, (ii) tested for the existence of behavioral syndrome in these species, and (iii) compared their performances using an open‐field test. Our results show that V. crabro foundresses behave consistently but not V. velutina; this lack of consistency being mainly due to reduced variance among individuals. This result questions the possibility of detecting consistent behavioral differences in species having recently undergone a strong bottleneck. Both species exhibit the same correlations between activity, boldness and exploration and V. velutina clearly outperforms V. crabro for all traits. Our results suggest that activity, boldness, and exploration are implicated in both hornet nest initiation and invasion process which contributed to explain why social hymenopterans are so successful at colonization.

Olfactory Attraction of the Hornet Vespa velutina to Honeybee Colony Odors and Pheromones

Since the beginning of the last century, the number of biological invasions has continuously increased worldwide. Due to their environmental and economical consequences, invasive species are now a major concern. Social wasps are particularly efficient invaders because of their distinctive biology and behavior. Among them, the yellow-legged hornet, Vespa velutina, is a keen hunter of domestic honeybees. Its recent introduction to Europe may induce important beekeeping, pollination, and biodiversity problems. Hornets use olfactory cues for the long-range detection of food sources, in this case the location of honeybee colonies, but the exact nature of these cues remains unknown. Here, we studied the orientation behavior of V. velutina workers towards a range of hive products and protein sources, as well as towards prominent chemical substances emitted by these food sources. In a multiple choice test performed under controlled laboratory conditions, we found that hornets are strongly attracted to the odor of some hive products, especially pollen and honey. When testing specific compounds, the honeybee aggregation pheromone, geraniol, proved highly attractive. Pheromones produced by honeybee larvae or by the queen were also of interest to hornet workers, albeit to a lesser extent. Our results indicate that V. velutina workers are selectively attracted towards olfactory cues from hives (stored food, brood, and queen), which may signal a high prey density. This study opens new perspectives for understanding hornets’ hunting behavior and paves the way for developing efficient trapping strategies against this invasive species.

Spatial distribution of Vespa velutina individuals hunting at domestic honeybee hives: heterogeneity at a local scale

Since its recent introduction into Europe, the yellow‐legged hornet, Vespa velutina, has become a major predator of the domestic honeybee, Apis mellifera, but little is known about its hunting behavior. We studied V. velutina hunting behavior by a capture‐mark‐recapture procedure in an experimental apiary. A total of 360 hornets were captured and tagged, and we determined: (i) the number of hornets visiting the apiary and the changes in time, (ii) the average number of individual visits per half‐day and the time elapsed between consecutive recaptures, and (iii) the individual and global distribution of the hornets in the apiary. More than 50% of the marked hornets were recaptured at least once, this increased to 74% in considering the first marked individuals. We estimated 350 hornets visiting the patch daily with at least 1 visit per half‐day. The number of marked hornets decreased over time while the number of unmarked ones increased, suggesting a turnover of individuals. The reduction of the delay between consecutive visits indicates that hornets became more efficient over time. Most of the hornets (88%) were recaptured in front of different hives but, overall, the global distribution was aggregative. Hornets were mainly recaptured in front of 1 hive which was neither the smallest nor the biggest colony, suggesting that the major cue used by hornets is not the amount of food. We hypothesize that the defensive behavior of the honeybee colony could explain our results which may be promising to further studies.

How Apis mellifera Behaves with its Invasive Hornet Predator Vespa velutina

Invasive species are now recognized as a major cause of native biodiversity loss worldwide. In the current deleterious context for pollinators, the invasive yellow-legged hornet, Vespa velutina, represents an additional threat to the domestic honeybee, Apis mellifera, in Europe. Therefore, understanding the impact of this predator on honeybee colonies is of major importance. In the present study, we tried to assess the impact of V. velutina on the honeybee foraging and defence behaviour based on the video monitoring of two hives. Balling behaviour is reported here for the first time under natural conditions in A. mellifera against V. velutina in Europe. Although these results are preliminary and should be carefully considered, we found that the number of hornets impacted honeybee foraging and defence behaviours. More defensive behaviours were notified in the hive, which survives slightly longer. This may suggest that selecting for more defensive colonies may provide an interesting perspective.

Comparison of reproductive traits of foundresses in a native and an invasive hornet in Europe

The population dynamics of annual social hymenoptera such as vespids depend largely on the fertility of the foundresses, which, in turn, is a key factor in the context of biological invasions. The native European hornet Vespa crabro (Vc) and the invasive Asian hornet Vespa velutina (Vv) have generally similar ecological traits, e.g. nesting and feeding habits, although they differ in colony size, which is higher in Vv. Furthermore, in contrast to Vc, Vv is more specialized in its predatory habits, intensively hunting honey bees at the hive. Comparing the morphological and reproductive traits of two closely related species occupying the same ecological niche, one of which is a native species and the other an alien, can help us to gain an understanding of the invasion process. To this end, we here compare reproductive (ovarian size and maturation, fat level, spermatheca size and sperm stock, fecundity) and morphological traits (head size, weight) of the foundresses of these two hornet species. We observed that ovarian maturation began approximately one month earlier in Vv than in Vc, and that the fat level in the former was lower. We found twice the number of sperm in the mated foundresses of Vv than in those of Vc (more than 100 × 103 and less than 50 × 103 sperm, respectively), in a 16% smaller spermatheca in Vc. Furthermore, the sperm of Vv was found to be 65% shorter than that of Vc. The precocity and higher potential fecundity of Vv queens may have favoured this species over Vc in terms of predatory behaviour, and thereby contributed to its invasiveness.