Explaining the reasons for the increased mortality of the honey bee (Apis mellifera L.) in recent years, in Europe and North America, has become a global research priority in apicultural science. Our project was aimed at determining the relationship between environmental conditions, beekeeping techniques, the epidemiological situation of pathogens, and the mortality rate of bee colonies. Dead bee samples were collected by beekeepers from 2421 colonies. The samples were examined for the presence of V. destructor, Nosema spp. (Nosema apis and Nosema ceranae), chronic bee paralysis virus (CBPV), acute bee paralysis virus (ABPV), deformed wing virus (DWV), and Israeli acute paralysis virus (IAPV).
Among the environmental and colony management factors under analysis, significant differences between apiaries with high (>10%), low (≤10%) or no losses of the colonies were only found in the case of the methods used by beekeepers to combat varroa mites. However, the epidemiological patterns in the case of V. destructor infestation and the DWV and ABPV infections highly differed. The data we obtained indicated that co-infections play a decisive role in the etiology of the significant collapse of colonies in apiaries in Poland. The main reason for this phenomenon can be described as strong infestation with V. destructor, followed by an intensive development of viral infections caused by DWV and (much less frequently) by ABPV. Despite a high prevalence of Nosema spp. microsporidia (with a dominant incidence of N. ceranae), a direct relationship between these parasites and the mortality rate of colonies was not proved.
The objective of the research was a comparative assessment of the infection levels of Nosema spp. in honey bees collected from different areas of the hive. A total of 588 honey bee colonies were sampled in spring (April-May) 2015 and 2016 through the simultaneous collection of dead worker bees from the bottom board of the hive and live bees from peripheral combs. A microscopic assay of composite samples of 60 bees was used for the detection and quantification of Nosema spp. spores. Consistent positive results of laboratory tests (detection of Nosema spp. spores in both live and dead bee samples) were achieved for 28% of colonies from surveyed group. In 36% of colonies both types of samples were Nosema-negative. Spores of Nosema spp. were detected solely in worker bees from the bottom board or exclusively in bees from nests in every 18% of sampled colonies. No differences were found between the share of colonies that had been identified as Nosema-infected on the basis of an analysis of only the live or dead bees (46% versus 46%). Laboratory examination of both types of bee samples can improve the reliability and accuracy of spore counting for the diagnosis of Nosema spp. infection in spring. The introduction of this sampling strategy in routine laboratory diagnostics can be considered as an alternative to the application of more sensitive PCR methods or sampling a higher number of live bees.
Screening of the prevalence of Paenibacillus larvae spores in honey bee colonies in apiaries from 162 districts, belonging to nine provinces was carried out during 2009-2011. The honey samples were examined by the use of a culture method. Based on the number of CFUs grown on Columbia sheep blood agar medium, the level of infection and probability of American foulbrood outbreak was estimated. Altogether, 6,510 pooled honey samples from 32,550 bee colonies located in 2,294 apiaries were collected. P. larvae was identified in 45% of the surveyed apiaries. The widest distribution of P. larvae was found in the Małopolskie province. Culture-positive honey samples were obtained for 71% of the apiaries and in a half of them, the level of spores was high. In the Warmińsko-Mazurskie province, the presence of the bacterium was detected in 58% of the apiaries. In the remaining provinces, from 26% to 47% of the apiaries were contaminated with P. larvae spores
The risk exposure of bee colonies to the toxicity of systemic neonicotinoid insecticides was assessed. Various methods of chemical prevention of commercial winter and spring oilseed rape crops in field-realistic conditions were taken into account in the assessment. Pesticides were applied in accordance with the actual agricultural practice. Commercial crop protection products with thiamethoxam, clothianidin or imidacloprid were used as seed treatment. Formulations containing acetamiprid or thiacloprid were used for spraying. Fifteen healthy bee colonies were placed in close proximity to each of the oilseed rape fields throughout the blooming period. During florescence, the samples of nectar (directly from flowers and nectar flow from combs) and pollen loads were collected repeatedly. Samples of honey, bee bread and adult bees were taken one week after the end of plants flowering. To ensure high specificity and sensitivity of analysed pestcicides modified QuEChERS extraction method and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used. The five of neonicotinoid insecticides (imidacloprid, clothianidin, thiametoxam, acetamiprid and thiacloprid) were analyzed in multi-residue method with 0.1 - 10 ng/g limits of detection. Palynological analysis was done to determine the botanical origin of the nectar, honey and pollen. Development of bee colonies (brood area, worker biomass, colony health) was assessed every 3 weeks until the end of the beekeeping season. The amount of pollen collected by bees per hive, bee bread area and rape honey yield was also measured. The long-term effects of insecticides on bees were estimated using the same methods in April of the following year.
All the neonicotinoid insecticides applied to control oilseed rape pests were present in the samples of nectar and pollen. Their residue levels were lower than the acute oral and contact LD50 values. Among five examined neonicotinoids, the most frequently detected were: thiamethoxam, thiacloprid and acetamiprid. These substances were present in 65, 64, and 51% of the nectar samples and in 37, 62, and 45% of the pollen samples, respectively. The highest level of residues were noted after the thiamethoxam seed treatment; on average, 4.2 and 3.8 ng/g in the nectar and pollen samples. In the nectar and pollen samples from winter rape fields, lower levels of neonicotinoid residues were found in comparison to spring rape samples. The contaminations of neonicotinoids applied as seed dressing in nectar samples were significantly higher in comparison to the pollen samples. No negative effects of neonicotinoids on the bee mortality, brood development, strength, and honey yield of healthy bee colonies were found throughout the study period. However, the risk exposure of bee colonies on adverse impact of pesticide residues is high in areas of intensively cultivated oilseed rape.
The effects to honeybee colonies (Apis mellifera L.) during and after exposure to flowering maize (Zea mays L.), grown from seeds coated with clothianidin and imidacloprid was assessed in field-realistic conditions. The experimental maize crops were adjacent to the other flowering agriculture plants. Honey bee colonies were placed in three differently protected maize fields throughout the blooming period, and thereafter they were transferred to a stationary apiary. Samples of pollen loads, bee bread, and adult bees were collected and analyzed for neonicotinoid residues. To ensure high specificity and sensitivity of detection of the analyzed pesticides, a modified QuEChERS extraction method and liquid chromatography coupled with tandem mass spectrometry were used. Clothianidin was detected only in the samples of pollen loads. Their residue levels ranged from 10.0 to 41.0 ng/g (average 27.0 ng/g). Imidacloprid was found in no investigated sample. No negative effects of neonicotinoid seed-treated maize on the development and long-term survival of honey bee colonies were observed. The low proportion of Zea mays pollen in total bee-collected pollen during the maize flowering period was noted. The findings suggest that maize plants are less attractive forage for honey bees than phacelia (Phacelia tanacetifolia Benth.), buckwheat (Fagopyrum Mill.), white clover (Trifolium repens L.), goldenrod (Solidago L.), and vegetation from Brassicaceae family.
The results indicate a possibility of reducing the risk of bees being exposed to the toxic effect of insecticidal dusts dispersed during maize sowing by seeding, in the areas surrounding maize crops, plants that bloom later in the year.