Pesticides in honey bee colonies: Establishing a baseline for real world exposure over seven years in the USA.

Honey bees Apis mellifera forage in a wide radius around their colony, bringing back contaminated food resources that can function as terrestrial bioindicators of environmental pesticide exposure. Evaluating pesticide exposure risk to pollinators is an ongoing problem. Here we apply five metrics for pesticide exposure risk (prevalence, diversity, concentration, significant pesticide prevalence, and hazard quotient (HQ)) to a nation-wide field study of honey bees, Apis mellifera in the United States. We examined samples from 1055 apiaries over seven years for 218 different pesticide residues and metabolites, determining that bees were exposed to 120 different pesticide products with a mean of 2.78 per sample. Pesticides in pollen were highly prevalent and variable across states. While pesticide diversity increased over time, most detections occurred at levels predicted to be of low risk to colonies. Varroacides contributed most to concentration, followed by fungicides, while insecticides contributed most to diversity above a toxicity threshold. High risk samples contained one of 12 different insecticides or varroacides. Exposures predicted to be low-risk were nevertheless associated with colony morbidity, and low-level fungicide exposures were tied to queen loss, Nosema infection, and brood diseases.

Social disruption: Sublethal pesticides in pollen lead to Apis mellifera queen events and brood loss.

Eusocial Apis mellifera colonies depend on queen longevity and brood viability to survive, as the queen is the sole reproductive individual and the maturing brood replenishes the shorter-lived worker bees. Production of many crops rely on both pesticides and bee pollination to improve crop quantity and quality, yet sublethal impacts of this pesticide exposure is often poorly understood. We investigated the resiliency of queens and their brood after one month of sublethal exposure to field relevant doses of pesticides that mimic exposure during commercial pollination contracts. We exposed full size colonies to pollen contaminated with field-relevant doses of the fungicides (chlorothalonil and propicanizole), insecticides (chlorypyrifos and fenpropathrin) or both, noting a significant reduction in pollen consumption in colonies exposed to fungicides compared to control. While we found no difference in the total amount of pollen collected per colony, a higher proportion of pollen to non-pollen foragers was detected in all pesticide exposed colonies. After ceasing treatments, we measured brood development, discovering a significant increase in brood loss and/or cannibalism across all pesticide exposed groups. Sublethal pesticide exposure in general was linked to reduced production of replacement workers and a change in protein acquisition (pollen vs. non-pollen foraging). Fungicide exposure also resulted in increased loss of the reproductive queen.

Social networks predict the life and death of honey bees.

In complex societies, individuals' roles are reflected by interactions with other conspecifics. Honey bees (Apis mellifera) generally change tasks as they age, but developmental trajectories of individuals can vary drastically due to physiological and environmental factors. We introduce a succinct descriptor of an individual's social network that can be obtained without interfering with the colony. This 'network age' accurately predicts task allocation, survival, activity patterns, and future behavior. We analyze developmental trajectories of multiple cohorts of individuals in a natural setting and identify distinct developmental pathways and critical life changes. Our findings suggest a high stability in task allocation on an individual level. We show that our method is versatile and can extract different properties from social networks, opening up a broad range of future studies. Our approach highlights the relationship of social interactions and individual traits, and provides a scalable technique for understanding how complex social systems function.

Varroa destructor: A Complex Parasite, Crippling Honey Bees Worldwide.

The parasitic mite, Varroa destructor, has shaken the beekeeping and pollination industries since its spread from its native host, the Asian honey bee (Apis cerana), to the naïve European honey bee (Apis mellifera) used commercially for pollination and honey production around the globe. Varroa is the greatest threat to honey bee health. Worrying observations include increasing acaricide resistance in the varroa population and sinking economic treatment thresholds, suggesting that the mites or their vectored viruses are becoming more virulent. Highly infested weak colonies facilitate mite dispersal and disease transmission to stronger and healthier colonies. Here, we review recent developments in the biology, pathology, and management of varroa, and integrate older knowledge that is less well known.

Colony Collapse Disorder (CCD) and bee age impact honey bee pathophysiology.

Honey bee (Apis mellifera) colonies continue to experience high annual losses that remain poorly explained. Numerous interacting factors have been linked to colony declines. Understanding the pathways linking pathophysiology with symptoms is an important step in understanding the mechanisms of disease. In this study we examined the specific pathologies associated with honey bees collected from colonies suffering from Colony Collapse Disorder (CCD) and compared these with bees collected from apparently healthy colonies. We identified a set of pathological physical characteristics that occurred at different rates in CCD diagnosed colonies prior to their collapse: rectum distension, Malpighian tubule iridescence, fecal matter consistency, rectal enteroliths (hard concretions), and venom sac color. The multiple differences in rectum symptomology in bees from CCD apiaries and colonies suggest effected bees had trouble regulating water. To ensure that pathologies we found associated with CCD were indeed pathologies and not due to normal changes in physical appearances that occur as an adult bee ages (CCD colonies are assumed to be composed mostly of young bees), we documented the changes in bees of different ages taken from healthy colonies. We found that young bees had much greater incidences of white nodules than older cohorts. Prevalent in newly-emerged bees, these white nodules or cellular encapsulations indicate an active immune response. Comparing the two sets of characteristics, we determined a subset of pathologies that reliably predict CCD status rather than bee age (fecal matter consistency, rectal distension size, rectal enteroliths and Malpighian tubule iridescence) and that may serve as biomarkers for colony health. In addition, these pathologies suggest that CCD bees are experiencing disrupted excretory physiology. Our identification of these symptoms is an important first step in understanding the physiological pathways that underlie CCD and factors impacting bee health.

In-hive Pesticide Exposome: Assessing risks to migratory honey bees from in-hive pesticide contamination in the Eastern United States.

This study measured part of the in-hive pesticide exposome by analyzing residues from live in-hive bees, stored pollen, and wax in migratory colonies over time and compared exposure to colony health. We summarized the pesticide burden using three different additive methods: (1) the hazard quotient (HQ), an estimate of pesticide exposure risk, (2) the total number of pesticide residues, and (3) the number of relevant residues. Despite being simplistic, these models attempt to summarize potential risk from multiple contaminations in real-world contexts. Colonies performing pollination services were subject to increased pesticide exposure compared to honey-production and holding yards. We found clear links between an increase in the total number of products in wax and colony mortality. In particular, we found that fungicides with particular modes of action increased disproportionally in wax within colonies that died. The occurrence of queen events, a significant risk factor for colony health and productivity, was positively associated with all three proxies of pesticide exposure. While our exposome summation models do not fully capture the complexities of pesticide exposure, they nonetheless help elucidate their risks to colony health. Implementing and improving such models can help identify potential pesticide risks, permitting preventative actions to improve pollinator health.

Queen and young larval pheromones impact nursing and reproductive physiology of honey bee (Apis mellifera) workers.

Several insect pheromones are multifunctional and have both releaser and primer effects. In honey bees (Apis mellifera), the queen mandibular pheromone (QMP) and e-beta-ocimene (eß), emitted by young worker larvae, have such dual effects. There is increasing evidence that these multifunctional pheromones profoundly shape honey bee colony dynamics by influencing cooperative brood care, a fundamental aspect of eusocial insect behavior. Both QMP and eß have been shown to affect worker physiology and behavior, but it has not yet been determined if these two key pheromones have interactive effects on hypopharyngeal gland (HPG) development, actively used in caring of larvae, and ovary activation, a component of worker reproductive physiology. Experimental results demonstrate that both QMP and eß significantly suppress ovary activation compared to controls but that the larval pheromone is more effective than QMP. The underlying reproductive anatomy (total ovarioles) of workers influenced HPG development and ovary activation, so that worker bees with more ovarioles were less responsive to suppression of ovary activation by QMP. These bees were more likely to develop their HPG and have activated ovaries in the presence of eß, providing additional links between nursing and reproductive physiology in support of the reproductive ground plan hypothesis.