Osmia Research Articles

The establishment and potential spread of Osmia cornuta (Hymenoptera: Megachilidae) in North America.

Mason bees, subgenus Osmia Panzer (Hymenoptera: Megachilidae), are economically and ecologically significant pollinators. In eastern North America, the rapid spread of 2 non-native species from Asia, Osmia cornifrons Radoszkowski and Osmia taurus Smith, has coincided with declines in native Osmia populations, raising concern about the effects of further exotic arrivals. Here we investigate the recent establishment in British Columbia, Canada of the European orchard bee, Osmia cornuta Latreille, previously thought to be limited to Europe and its periphery. We document O. cornuta records ranging more than 170 km, including sightings of live adults and the discovery of a multigenerational nest with hundreds of cocoons. We tested whether these cocoons could be discriminated from other Osmia species by training a machine learning classifier on features extracted from images. The best performing model could not reliably discriminate cocoons by species, raising the possibility O. cornuta could be inadvertently intermingled in future commercial shipments. Recent occurrence records of O. cornifrons and O. taurus were spatially isolated, suggesting ongoing anthropogenic dispersal of these species. We predicted the suitability of North American habitats for O. cornuta by estimating its native climate niche. This analysis indicated broad regions of the Pacific Northwest and eastern North America contain potentially suitable habitat. Our findings document the establishment of O. cornuta in North America and the potential for its expansion. Our study demonstrates the utility of accessible biodiversity data archives and public observation programs in tracking non-native species spread and highlights the need for future monitoring of exotic Osmia.

A test method for assessing chronic oral toxicity of a pesticide to solitary nesting orchard bees, Osmia spp. (Hymenoptera: Megachilidae).

Orchard bees of the genus Osmia Panzerare important pollinators of fruit trees in various regions of the world, with some species commercially available in the United States and Europe. In addition to their pollination services, Osmia lignaria, Osmia cornifrons, Osmia bicornis, and Osmia cornuta have been identified as potential model species for solitary bees in pesticide risk assessment and have been used for the development of new methods to test acute lethal effects via contact and oral routes of exposure. Our goal was to expand the available methodology to characterize the toxicity of pesticides for these solitary bees through a chronic oral test for adult bees. Chronic oral toxicity of pesticides to orchard bees has been reported, but methods differ among research groups. In our study, O. lignaria, O. cornifrons, O. bicornis, and O. cornuta female bees had access to sucrose solution ad libitum in separate, species-specific 10-day tests. Mean body mass, mean daily consumption, and survival differed among the studied bee species. The dose-response test design was validated with dimethoate, a reference toxic compound, and chronic toxicity endpoints were estimated for the 4 Osmia species. The median lethal daily doses normalized by weight for O. lignaria, O. bicornis, O. cornuta, and O. cornifrons were within the same order of magnitude at 0.23, 0.26, 0.49, and 0.61 µg dimethoate/g bee/day, respectively. The methodology described here was aligned as much as possible with the available honey bee and bumble bee standard methods to facilitate the comparison of chronic toxicity profiles among bee species.

Bee sensitivity derived from acute contact tests biased by standardised protocols?

In an acute contact test with bees the compound of interest is dissolved in a carrier solvent (frequently acetone) and then a droplet of the solution is placed on the dorsal thorax of the bee. The volume of the droplet is standardised to 1 µL for honeybees and to 2 µL for bumblebees. In practice the same droplet volume is used for bees with very different sizes. In this research the effect of the droplet volume was evaluated with acute contact tests with dimethoate for the alfalfa leafcutter bee, the red mason bee, the honeybee and the bumblebee. The results were analysed with a ToxicoKinetic ToxicoDynamic (TKTD) model to separate kinetic from dynamic effects. This allows to compare the sensitivity of the bee based on the effect threshold and not on the time, species and test dependent LD50s. The analysis of the test results indicates that the magnitude of the response of the bees increased with increasing droplet size. The results also showed that the manifestation of effects over time is slower for the red mason bee and the bumblebee compared to the honeybee and the alfalfa leafcutter bee. This implies that the result of a 2 day test with a fixed dosing volume results in different response for a bumblebee compared to the alfalfa leafcutter bee, not because of different sensitivities of the bees involved but due to the difference of relative dosed surface ratio. So comparing the sensitivity of bee species, based on standardised tests is biased and amplifies the sensitivity for the smaller bee species.

SolBeePopecotox: A Population Model for Pesticide Risk Assessments of Solitary Bees.

In agricultural landscapes, solitary bees occur in a large diversity of species and are important for crop and wildflower pollination. They are distinguished from honey bees and bumble bees by their solitary lifestyle as well as different nesting strategies, phenologies, and floral preferences. Their ecological traits and presence in agricultural landscapes imply potential exposure to pesticides and suggest a need to conduct ecological risk assessments for solitary bees. However, assessing risks to the large diversity of managed and wild bees across landscapes and regions poses a formidable challenge. Population models provide tools to estimate potential population-level effects of pesticide exposures, can support field study design and interpretation, and can be applied to expand study data to untested conditions. We present a population model for solitary bees, SolBeePopecotox, developed for use in the context of ecological risk assessments. The trait-based model extends a previous version with the explicit representation of exposures to pesticides from relevant routes. Effects are implemented in the model using a simplified toxicokinetic-toxicodynamic model, BeeGUTS (GUTS = generalized unified threshold model for survival), adapted specifically for bees. We evaluated the model with data from semifield studies conducted with the red mason bee, Osmia bicornis, in which bees were foraging in tunnels over control and insecticide-treated oilseed rape fields. We extended the simulations to capture hypothetical semifield studies with two soil-nesting species, Nomia melanderi and Eucera pruinosa, which are difficult to test in empirical studies. The model provides a versatile tool for higher-tier risk assessments, for instance, to estimate effects of potential exposures, expanding available study data to untested species, environmental conditions, or exposure scenarios. Environ Toxicol Chem 2024;00:1-17. © 2024 SETAC.

Conventional agriculture affects sex communication and impacts local population size in a wild bee

Man-made agricultural stressors have been identified to compromise the reproductive dynamics of bee populations within agricultural environments. With the aid of bee hotels, we explored the influence of conventional and organic farming systems on local population size and body traits of the mason bee, Osmia bicornis, in southern Germany. We further used a chemical ecology approach and bioassays to test whether farming management influence male pre-copulatory behaviors. We observed a positive relationship between the extent of organic agriculture in the landscape and both overall brood cell production and nesting frequency. Moreover, farming systems were found to influence body traits, with bees from organic sites being smaller in size and having a different cuticular hydrocarbon composition compared with those at conventional sites. Bioassays revealed that males were more sexually attracted to freeze-killed females from conventional sites compared with those from organic sites. Intriguingly, treating females from organic fields with synthetic semiochemicals enhanced their sexual attraction to levels comparable with females from conventional sites. Our findings shed light on the intricate interplay between farming practices and the reproductive behaviors of wild mason bees, emphasizing the need for a comprehensive understanding of these dynamics for effective conservation and management strategies.

Elevated atmospheric CO2 alters the multi-element stoichiometry of pollen-bearing oak flowers, with possible negative effects on bees

Increasing atmospheric CO2 levels change the elemental composition in plants, altering their nutritional quality and affecting consumers and ecosystems. Ecological stoichiometry provides a framework for investigating how CO2-driven nutrient dilution in pollen affects bees by linking changes in pollen chemical element proportions to the nutritional needs of bees. We investigated the consequences of five years of Free Air CO2 Enrichment (FACE) in a mature oak-dominated temperate forest on the elemental composition of English oak (Quercus robur) pollen. We measured the concentrations and proportions of 12 elements (C, N, P, S, K, Na, Ca, Mg, Cu, Zn, Fe, and Mn) in Q. robur pollen-bearing flowers collected from the Birmingham Institute for Forest Research (BIFoR) FACE facility. An elevated CO2 (eCO2) level of 150 ppm above ambient significantly reduced the S, K, and Fe levels and altered the multi-element ratio, with different elements behaving differently. This shift in pollen multi-element composition may have subsequent cascading effects on higher trophic levels. To assess the impact on bees, we calculated the stoichiometric mismatch (a measure of the discrepancy between consumer needs and food quality) for two bee species, Osmia bicornis (red mason bee) and Apis mellifera (honey bee), that consume oak pollen in nature. We observed stoichiometric mismatches for P and S, in pollen under eCO2, which could negatively affect bees. We highlight the need for a comprehensive understanding of the changes in pollen multi-element stoichiometry under eCO2, which leads to nutrient limitations under climate change with consequences for bees.

Application of the solitary red mason bee, Osmia rufa L. (syn. O. bicornis), in forest monocultures in Poland

Seed orchards are utilised in forestry to avoid monoculture cultivation in forest areas and also constitute a gene bank for various tree species. In order to meet seed needs, preserve species diversity and genetic resources of forest management of the country, several hundred seed orchards served the purposes in Poland today. The paper presents an innovative solution to increase tree yield by introducing nests of solitary bees Osmia rufa L. (syn. O. bicornis) into monocultures. These insects are a natural solution that allows increasing the yield of selected tree and shrub species, especially fruit trees and shrubs and selected forest species. In order to determine the suitability of Osmia rufa L. to support the seed production process, a several-year research project was pursued consisting in assessing the quality of seeds, bee reproduction and identifying natural populations of insects in forest areas that were already present there before the introduction of bees. The research clearly shows that red mason bee, Osmia rufa L., can be employed with great success in forest areas to increase the productivity of selected forest tree species. Additionally, the work presents the results of study of red mason bee reproduction, showing that these bees in forest areas can also develop properly. Keywords: seed orchards; Tilia cordata; Quercus petraea; Prunus avium; insects; rearing of bees

Honey bees and mason bees as biological indicators of landscape pesticide loads: Different results but similar conclusions

Agricultural environments, including crop and non-crop areas, often provide important pollen and nectar resources for managed and wild bees. However, these resources may be contaminated with pesticides detrimental to bees and other non-target organisms, including humans. Differences in life-history traits among bee species influence food resource exploitation and pesticide exposure. This study assesses the potential of honey bees (Apis mellifera) and mason bees (Osmia), two bee species with highly contrasting functional traits, as biological indicators of pesticide exposure in 34 Italian agricultural farms. Pollen loads of both species were used to identify pollen species collected and to analyse multi-residue levels of pesticides. Pesticide risk indexes were calculated for honey bees, mason bees and humans. In mason bees, pesticide risk was not influenced by plant diversity. In agreement with their pollen preferences and short foraging ranges, mason bees collected a high proportion of pollen from flowers of the target crop. Conversely, pesticide risk decreased with increasing pollen diversity in honey bees. In agreement with their generalist foraging habits and long foraging ranges honey bees collected a greater diversity of pollen species and a lower proportion of target crop pollen. Although honey bees and mason bees showed similar toxic loads and pesticide composition, at a field scale pesticide risk of one species is not a good indicator of the risk to the other species. Our study confirms that bees in agricultural environments are pervasively exposed to multi-residue pesticide loads. Exposure is conditioned by specific bee traits but is also highly context-dependent.

A Comprehensive Review on Entomovectoring in Agroecosystem

Protecting beneficial arthropods is essential, as they provide crucial services beyond pollination, including disease and insect pest management. The combination of several ecosystem services for agricultural sustainability requires the recognition that biodiversity is coupled with bio-complexity, productivity, resilience, and ecosystem functionality. Insects such as bumblebees, mason bees, and honey bees have long been employed professionally for pollination, likewise microbial biocontrol agents are frequently employed in pest management. A key aspect of pollination ecology is entomovectoring technology that utilizes managed bees to disseminate biocontrol agents to flowering crops. This can enhance crop yields by providing non-chemical protection against pests and diseases as well as enhancing pollination efficiency. This technology is based on bee management, manipulation of bee behaviour, components of cropping system, plant-pathogen-vector-antagonist system which can be a trend-breaking pest management system in agriculture and will give double benefit to agriculture i.e. crop pollination and crop protection acting together for increased crop yield and quality.

Osmia lignaria (Hymenoptera: Megachilidae) increase pollination of Washington sweet cherry and pear crops.

Apis mellifera Linnaeus (Hymenoptera: Apis), honey bees, are the most widely used managed crop pollinators. However, their high rental cost and uncertain availability for North American orchard crops have motivated growers to explore alternative pollination options. We examined whether adding solitary, spring-flying Osmia lignaria Say (Hymenoptera: Megachilidae), blue orchard bees, as co-pollinators with A. mellifera in Washington sweet cherry and pear orchards enhances fruit set and yield compared to the use of A. mellifera alone. We added managed O. lignaria to orchard sites where A. mellifera hives were already present. Fruit set, fruit yield, and O. lignaria reproduction at O. lignaria-supplemented sites were compared to nearby, paired sites pollinated only by A. mellifera (3 paired cherry and 3 paired pear sites). For both crops, the addition of O. lignaria significantly increased fruit set but did not yield at harvest. Microscopic inspection of pollen grains from O. lignaria nest cell provisions confirmed that O. lignaria primarily visited orchard flowers. Mean retention of O. lignaria in cherry orchards was slightly higher (65%) than O. lignaria retention reported in other orchard crops (30%-60%). However, retention in pear orchards was much lower (≤20%). These results show that supplementing hives with O. lignaria in Washington spring orchard crops can increase overall pollination, but that trees fail to bear developing fruit to maturity. The strategy of using co-pollinators, O. lignaria and A. mellifera, in US orchards may act as "pollination insurance" when A. mellifera hives are in low supply or when the weather is not amenable for A. mellifera flight during the bloom period.

Influence of agricultural intensification on pollinator pesticide exposure, food acquisition and diversity

Abstract Pollinators are essential for maintaining sustainable crop production, while the decline of pollinators is a widespread concern. Agricultural intensification is one of the primary drivers of the decline of insect pollinators. Agricultural intensification usually involves a decreasing of non‐crop semi‐natural habitat and an increasing of pesticide exposure for pollinators. However, causal links between agricultural intensification, increased pesticide exposure, and reduced pollinator's food sources and pollinator diversity remain underexplored. We assessed pollinator diversity across a landscape gradient where the proportion of rice ranged from 11% to 85% in South China. We placed honeybee (Apis mellifera) and mason bee (Osmia excavata) in these landscapes and investigated pesticide exposure in honeybee foragers and pollen, and in mason bee pollen and nesting materials. We also assessed the acquisition of food by mason bees. We found a higher frequency of pesticide detection in honeybee foragers and honeybee pollen samples in areas with a higher proportion of rice fields. There was a strong positive relationship between mason bee food acquisition and the proportion of semi‐natural habitats, while no significant effects of pesticide exposure on pollinator diversity were found in addition to the effect of semi‐natural habitat. Synthesis and applications: Our results suggest that pollinator communities could be at an increased risk of pesticide exposure due to intensified agriculture, while the negative impact on pollinator diversity mainly results from the loss of habitat and/or reduced food sources. This study highlights the importance of conserving semi‐natural habitat to mitigate the causes of decline in pollinator diversity. We also recommend long‐term, multi‐year studies to further understand the mechanisms behind the loss of pollinators in farming landscapes.

Osmia3DNest—Novel designed 3D printed artificial nest for solitary cavity‐nesting bees

Abstract The availability and appropriateness of nesting sites significantly influence the reproductive success and overall welfare of wild bees. Human‐induced factors contribute to the destruction of natural nesting habitats. To address these limitations, innovative solutions such as the development of artificial nests, offer alternative nest sites to support wild bee populations. We designed the Osmia3DNest, a 3D printed standardized nest tube for solitary cavity‐nesting bees, aiming to provide a safe for the environment, long‐life, time‐saving and biodegradable product that anyone can print. We proudly present the two Osmia3DNest models for mason bees—closed and open—using polylactic acid filament. We demonstrate the effectiveness of Osmia3DNest on mason bee reproduction parameters compared with traditional reed nests. Osmia3DNest can be an alternative to the other artificial nests, which people can customize for their necessity depending on their place of living (rural or urban area), and they can also be washed and reused several times and then decomposed. Osmia3DNest holds potential for wildlife biologists, management of pollinators, and educational outreach, offering adaptability for different bee species and experimental needs.

Microbiome diversity and composition across development stages of the Blue Orchard Bee, Osmia lignaria (Megachilidae)

Microbiome diversity and composition across development stages of the Blue Orchard Bee, Osmia lignaria (Megachilidae)

Attractant spray enhances nesting preference and reduces macroparasite infestation of Osmia cornuta

AbstractMason bees (Osmia. spp) can provide an alternative for crop pollination management in addition to the Western honeybees (Apis mellifera). Targeted evidence‐based guidelines can improve cost‐effective management of mason bees. Here, I test the effect of an attractant spray developed in the United States for improving the nesting preference for artificial trap nests of mason bees in Belgium. More specifically, this study investigates the effect of the attractant spray on the nesting preference and nesting performance of the European orchard bee (Osmia cornuta), as well as its effect on the infestation of nest‐associated macroparasites. The number of sealed nesting cavities was twice as high in the trap nests that were treated with the attractant spray. Nesting performance expressed as number of brood cells per cavity, successful cocoon formation, adult emergence, proportion of female bees in the offspring and the number of dead larvae was not different between the treated and the untreated nests. Overall infestation of macroparasites, and infestation of drosophilid flies in particular, were both twice as high in untreated nests. This study provides evidence that the attractant spray improves nesting preference and reduces macroparasite infestation in O. cornuta. The use of this attractant can provide growers and stakeholders with an effective management strategy to prevent infestation by macroparasites and promote efficient bee breeding.

Evaluation of the Pollination Efficiency of Apple Trees by Osmia excavata Alfken (Hymenoptera: Megachilidae).

The mason bee Osmia excavata Alfken is an apple pollinating insect widely distributed in northern China, in order to effectively utilize the mason bee and improve the pollination rate of apples, there is a need to evaluate the pollination efficiency of the bees. This study evaluated the pollination efficiency of the mason bee on apple orchards in Jinan and Yantai, Shandong Province, China. The study compared natural pollination areas and pollination areas with different release densities of O. excavata in terms of the effects of bee density, timing of pollination, and distance effects on fruit set rate, fruit shape index, fruit shape skewness, fruit soluble solids content, and fruit firmness. The optimal release density of bees was 6000 cocoons per hectare, resulting in the highest fruit setting rate of apple lateral flowers. From 07:00 to 14:00 was the best time for bee pollination. The optimal distance of hives from apple trees for pollination by O. excavata was 60m. Single fruit weight was significantly higher and fruit unsymmetrical rate, partial slope and hardness were all significantly lower at the release densities of 6000 or 12000 cocoons per hectare compared with 3000 cocoons per hectare or under natural pollination conditions. There was no significant difference in the content of soluble solids under different release densities. Thus, the radius of 60m from the hive was the effective pollination range and 6000 cocoons per hectare of mason bees could ensure the fruit quality of apple.

Monitoring fast‐moving animals—Building a customized camera system and evaluation toolset

Abstract Automated cameras (including camera traps) are an established observation tool, allowing, for example the identification of behaviours and monitoring without harming organisms. However, limitations including imperfect detection, insufficient data storage and power supply restrict the use of camera traps, making inexpensive and customizable solutions desirable. We describe a camera system and evaluation toolset based on Raspberry Pi computers and YOLOv5 that can overcome those shortcomings with its modular properties. We facilitate the set‐up and modification for researchers via detailed step‐by‐step guides. A customized camera system prototype was constructed to monitor fast‐moving organisms on a continuous schedule. For testing and benchmarking, we recorded mason bees (Osmia cornuta) approaching nesting aids on 20 sites. To efficiently process the extensive video material, we developed an evaluation toolset utilizing the convolutional neural network YOLOv5 to detect bees in the videos. In the field test, the camera system performed reliably for more than a week (2 h per day) under varying weather conditions. YOLOv5 detected and classified bees with only 775 original training images. Overall detection reliability varied depending on camera perspective, site and weather conditions, but a high average detection precision (78%) was achieved, which was confirmed by a human observer (80% of algorithm‐based detections confirmed). The customized camera system mitigates several disadvantages of commercial camera traps by using interchangeable components and incorporates all major requirements a researcher has for working in the field including moderate costs, easy assembly and an external energy source. We provide detailed user guides to bridge the gap between ecology, computer science and engineering.

Fungicide ingestion reduces net energy gain and microbiome diversity of the solitary mason bee

Fungicides are frequently used during tree fruit bloom and can threaten insect pollinators. However, little is known about how non-honey bee pollinators such as the solitary bee, Osmia cornifrons, respond to contact and systemic fungicides commonly used in apple production during bloom. This knowledge gap limits regulatory decisions that determine safe concentrations and timing for fungicide spraying. We evaluated the effects of two contact fungicides (captan and mancozeb) and four translaminar/plant systemic fungicides (cyprodinil, myclobutanil, penthiopyrad, and trifloxystrobin) on larval weight gain, survival, sex ratio, and bacterial diversity. This assessment was carried out using chronic oral ingestion bioassays where pollen provisions were treated with three doses based on the currently recommended field use dose (1X), half dose (0.5X), and low dose (0.1X). Mancozeb and penthiopyrad significantly reduced larval weight and survival at all doses. We then sequenced the 16S gene to characterize the larvae bacteriome of mancozeb, the fungicide that caused the highest mortality. We found that larvae fed on mancozeb-treated pollen carried significantly lower bacterial diversity and abundance. Our laboratory results suggest that some of these fungicides can be particularly harmful to the health of O. cornifrons when sprayed during bloom. This information is relevant for future management decisions about the sustainable use of fruit tree crop protection products and informing regulatory processes that aim to protect pollinators.

Systemic pesticides in a solitary bee pollen food store affect larval development and increase pupal mortality

Solitary bees are often exposed to various pesticides applied for pest control on farmland while providing pollination services to food crops. Increasing evidence suggests that sublethal toxicity of agricultural pesticides affects solitary bees differently than the social bees used to determine regulatory thresholds, such as honey bees and bumblebees. Studies on solitary bees are challenging because of the difficulties in obtaining large numbers of eggs or young larvae for bioassays. Here we show the toxic and sublethal developmental effects of four widely used plant systemic pesticides on the Japanese orchard bee (Osmia cornifrons). Pollen food stores of this solitary bee were treated with different concentrations of three insecticides (acetamiprid, flonicamid, and sulfoxaflor) and a fungicide (dodine). Eggs were transplanted to the treated pollen and larvae were allowed to feed on the pollen stores after egg hatch. The effects of chronic ingestion of contaminated pollen were measured until adult eclosion. This year-long study revealed that chronic exposure to all tested pesticides delayed larval development and lowered larval and adult body weights. Additionally, exposure to the systemic fungicide resulted in abnormal larval defecation and increased mortality at the pupal stage, indicating potential risk to bees from fungicide exposure. These findings demonstrate potential threats to solitary bees from systemic insecticides and fungicides and will help in making policy decisions to mitigate these effects.

Risk assessment requires several bee species to address species-specific sensitivity to insecticides at field-realistic concentrations

In the European registration process, pesticides are currently mainly tested on the honey bee. Since sensitivity data for other bee species are lacking for the majority of xenobiotics, it is unclear if and to which extent this model species can adequately serve as surrogate for all wild bees. Here, we investigated the effects of field-realistic contact exposure to a pyrethroid insecticide, containing lambda-cyhalothrin, on seven bee species (Andrena vaga, Bombus terrestris, Colletes cunicularius, Osmia bicornis, Osmia cornuta, Megachile rotundata, Apis mellifera) with different life history characteristics in a series of laboratory trials over two years. Our results on sensitivity showed significant species-specific responses to the pesticide at a field-realistic application rate (i.e., 7.5 g a.s./ha). Species did not group into distinct classes of high and low mortality. Bumble bee and mason bee survival was the least affected by the insecticide, and M. rotundata survival was the most affected with all individuals dead 48 h after application. Apis mellifera showed medium mortality compared to the other bee species. Most sublethal effects, i.e. behavioral abnormalities, were observed within the first hours after application. In some of the solitary species, for example O. bicornis and A. vaga, a higher percentage of individuals performed some abnormal behavior for longer until the end of the observation period. While individual bee weight explained some of the observed mortality patterns, differences are likely linked to additional ecological, phylogenetic or toxicogenomic parameters as well. Our results support the idea that honey bee data can be substitute for some bee species’ sensitivity and may justify the usage of safety factors. To adequately cover more sensitive species, a larger set of bee species should be considered for risk assessment.

Moderate use of pesticides in allotment gardens as indicated by their residues in larval food provisions of Osmia solitary bees

Exposure to pesticides may jeopardize pollinators, but it has rarely been examined in urban landscapes. We used larval food provisions (mix of pollen and nectar) of mason bees (Osmia spp.) nested in artificial shelters as matrices to investigate the rate of pesticide pollution in twelve allotment sites in Prague and Brno cities. Seven commercial croplands (fruit orchards, oilseed rape fields) were selected for comparison. In total, 79 samples of larval provisions were analysed using a validated UPLC–MS/MS method for the presence of 262 pesticides and/or important metabolites. Fifty-six pesticide residues were detected in the allotments and 74 in cropland sites. Fifty pesticide compounds were common to both landscapes. Fewer residues were found in the allotments (14.3 ± 0.9, mean ± SE) than in croplands (21.5 ± 1.1, mean ± SE; df = 17.4; t = −2.9; p < 0.01), and they were present at low levels up to 16 ppb. In cropland sites, ten residues occurred at high individual concentrations (mean per site > 10 ppb). The highest levels were observed for the fungicide pyrimethanil (mean = 1,989 ppb, maximum = 3,983 ppb) and among insecticides for thiacloprid (mean = 136 ppb, maximum = 170 ppb). The results supported the presumption of a lower risk of pesticide exposure in urban gardens than in croplands. Given the limited knowledge on the sublethal effects of pesticides and especially pesticide mixtures on solitary bee development, the regulation or control of pesticide use in allotment gardens is recommended.