Aim Invasive alien species (IAS) are recognized as major drivers of biodiversity loss, but few causal relationships between IAS and species declines have been documented. In this study, we compare the distribution (Belgium and Britain) and abundance (Belgium, Britain and Switzerland) of formerly common and widespread native ladybirds before and after the arrival of Harmonia axyridis, a globally rapidly expanding IAS. Location EuropeMethods We used generalized linear mixed-effects models (GLMMs) to assess the distribution trends of eight conspicuous and historically widespread and common species of ladybird within Belgium and Britain before and after the arrival of H. axyridis. The distribution data were collated largely through public participatory surveys but verified by a recognized expert. We also used GLMMs to model trends in the abundance of ladybirds using data collated through systematic surveys of deciduous trees in Belgium, Britain and Switzerland.Results Five (Belgium) and seven (Britain) of eight species studied show substantial declines attributable to the arrival of H. axyridis. Indeed, the two-spot ladybird, Adalia bipunctata, declined by 30% (Belgium) and 44% (Britain) over 5 years after the arrival of H. axyridis. Trends in ladybird abundance revealed similar patterns of declines across three countries.Main conclusion Together, these analyses show H. axyridis to be displacing native ladybirds with high niche overlap, probably through predation and competition. This finding provides strong evidence of a causal link between the arrival of an IAS and decline in native biodiversity. Rapid biotic homogenization at the continental scale could impact on the resilience of ecosystems and severely diminish the services they deliver.

As in many other locations in the world, honeybee colony losses and disorders have increased in Belgium. Some of the symptoms observed rest unspecific and their causes remain unknown. The present study aims to determine the role of both pesticide exposure and virus load on the appraisal of unexplained honeybee colony disorders in field conditions. From July 2011 to May 2012, 330 colonies were monitored. Honeybees, wax, beebread and honey samples were collected. Morbidity and mortality information provided by beekeepers, colony clinical visits and availability of analytical matrix were used to form 2 groups: healthy colonies and colonies with disorders (n = 29, n = 25, respectively). Disorders included: (1) dead colonies or colonies in which part of the colony appeared dead, or had disappeared; (2) weak colonies; (3) queen loss; (4) problems linked to brood and not related to any known disease. Five common viruses and 99 pesticides (41 fungicides, 39 insecticides and synergist, 14 herbicides, 5 acaricides and metabolites) were quantified in the samples.The main symptoms observed in the group with disorders are linked to brood and queens. The viruses most frequently found are Black Queen Cell Virus, Sac Brood Virus, Deformed Wing Virus. No significant difference in virus load was observed between the two groups. Three acaricides, 5 insecticides and 13 fungicides were detected in the analysed samples. A significant correlation was found between the presence of fungicide residues and honeybee colony disorders. A significant positive link could also be established between the observation of disorder and the abundance of crop surface around the beehive. According to our results, the role of fungicides as a potential stressor for honeybee colonies should be further studied, either by their direct and/or indirect impacts on bees and bee colonies.

Over a period of less than 5 years, Belgium was thoroughly invaded by the multicolored Asian coccinellid, Harmonia axyridis. At the same time, a decline of some native coccinellid species was observed in tree habitats. One hypothesis about the cause of this decline was that it might have been due to intraguild predation (IGP) by H. axyridis. In natural conditions, IGP between coccinellids can be tracked by using defensive compounds. Exogenous alkaloids in H. axyridis were therefore examined by gas chromatography-mass spectrometry (GC-MS), using individuals sampled from lime trees that were also occupied by other species of coccinellids. Harmonia axyridis was the dominant species at all life stages, in terms of both numbers of sites occupied and local abundance. The GC-MS analysis of H. axyridis larvae revealed traces of exogenous alkaloids from 19 of the 20 sites and, in nine of those 19 sites, more than 30% of the larvae analyzed contained exogenous alkaloids. Three alkaloids were detected: adaline from Adalia spp., calvine from Calvia spp. and propyleine from Propylea quatuordecimpunctata. Predation by H. axyridis on two different coccinellid species was also detected in the same larva, reinforcing the status of H. axyridis as a top predator. A generalized linear model indicated that IGP frequency was positively influenced by two variables: the abundance of extraguild and intraguild prey; and the interaction between these two variables. Our results therefore support the hypothesis that IGP by H. axyridis on native coccinellids in tree habitats has led to the decline of several of these species.

To evaluate the risks of pesticides for pollinators, we must not only evaluate their toxicity but also understand how pollinators are exposed to these xenobiotics in the field. We focused on this last point and modeled honey bee exposure to pesticides at the landscape level. Pollen pellet samples (n = 60) from 40 Belgian apiaries were collected from late July to October 2011 and underwent palynological and pesticide residue analyses. Areas of various crops around each apiary were measured at 4 spatial scales. The most frequently detected pesticides were the fungicides boscalid (n = 19, 31.7%) and pyrimethanil (n = 10, 16.7%) and the insecticide dimethoate (n = 10, 16.7%). We were able to predict exposure probability for boscalid and dimethoate by using broad indicators of cropping intensity, but it remained difficult to identify the precise source of contamination (e.g. specific crops in which the use of the pesticide is authorized). For pyrimethanil, we were not able to build any convincing landscape model that could explain the contamination. Our results, combined with the late sampling period, strongly suggest that pesticides applied to crops unattractive to pollinators, and therefore considered of no risk for them, may be sources of exposure through weeds, drift to neighboring plants, or succeeding crops.Pollinators like bees cover very large areas every day, visiting numerous plants for nectar, pollen, or gum collection and water sources. So doing, they also unintentionally collect airborne particles or substances diluted in the air. This has lead to using honey bees, a species often used as a model, and beekeeping products as biological indicators for environmental monitoring [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Monitoring of exposure to various environmental contaminants has already been carried out; these contaminants include heavy metals 2,5,14,15,17 , pesticides 3, 4, 11-13 , polycyclic aromatic hydrocarbons 6, 7, 9, 10, 18 and radioactivity 16 . Unfortunately, it is often not possible to identify the specific sources of contamination.The exposure of honey bees to pesticides has been linked to increased probability of colony disorders and losses [19][20][21] , alone or in combination with other stress-creating factors like poor nutrition or pathogen and parasite loads [22][23][24] . For this reason, it is crucial to understand the possible exposure pathways of honey bees to pesticides once they are released in the environment. Pesticide risk assessment is not just about the evaluation of the toxicity of the products. Ideally, we should also be able to accurately estimate how living organisms will be exposed to these products in the environment.Efforts to model the exposure of bees to pesticides have been carried out recently for risk assessment purposes. Some models aim to estimate direct contact exposure for spray applications 25 , while others have focused on contact exposure through dust 26 or on estimating pesticide intake [27][28][29] . Several routes of exposure are t...