Project : USDA ARS

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Research Project: Conduct Longitudinal Studies on Colony Performance and Explore Near-term Effects of Nutritional and Agrochemical Stressors on Honey Bee Health

Location: Invasive Species and Pollinator Health

2025 Annual Report

Objectives
As pollinators, honey bees (Apis mellifera) are the third most important agricultural livestock after cattle and pork, indispensable for crop production and global food security. Despite their significant economic importance, honey bees continue to face debilitating challenges from several interactive factors including poor nutrition, exposure to agrochemicals, reduced genetic diversity, devastating pests and pathogens and ongoing changes to climatic conditions. A common underlying thread is that these factors vary across seasons and across years, and their build-up leads to compounding impacts that result in patterns not easily discerned with short-term datasets. Depending on agricultural practices, some of the factors may go through cyclical trends that affect long-term performance of apiaries. To get a comprehensive understanding of factors determining honey bee health, it is necessary to obtain continuous recording of data on colony performance, survivorship, environmental factors surrounding the apiaries, agrochemical residues, and availability of nutritional forage, over long periods of time. This project will establish a Long-Term Honey Bee Research (LTHBR) system in California at the Davis ARS location, associated with the Invasive Species and Pollinator Health Research (ISPHR) unit. This LTHBR system will elucidate how key components involved in honey bee health and pollinator sustainability interact with the demand for pollination and agricultural practices. The data collected will generate insights into whether sustainable intensification of beekeeping can occur through better mitigation of stress-induced hive declines. This LTHBR system will also support the development of research projects that monitor a range of environmental conditions and correlated episodic events such as changes to nutrient flow, pest-pathogen cycles, and changing weather patterns affecting hive performance. The data collected over several years will enable the development and validation of theoretical and empirical models to forecast colony performance across various scenarios, allowing for strategies to improve pollinator health and sustainability. The following are the objectives and sub-objectives of the project plan: Objective 1: Establish longitudinal monitoring of apiaries to collect long-term data on colony performance and evaluate relative benefits of new management discoveries to improve honey bee health. Sub-objective 1A: Establish a Long-Term Honey Bee Research (LTHBR) system in California. Sub-objective 1B: Quantify the expression of hygienic behavior across the cooperator apiaries in the LTHBR system. Objective 2: Understand the effects of nutritional and agrochemical stressors on honey bee health and develop hive management strategies. Sub-objective 2A: Determine performance of honey bees under nutrient conditions relevant to California agriculture. Sub-objective 2B: Characterize how exposure to agrochemical stressors like IGRs affect honey bee reproduction, development and long-term colony stability to help beekeepers predict and mitigate the long-term consequences of agrochemical exposure.

Approach
The primary objective of this project plan is to conduct longitudinal monitoring of apiaries and collect long-term data on colony performance. As a part of Sub-objective 1A, the LTHBR system will be established in California in collaboration with commercial beekeepers, such that the different monitoring locations will be spread over the different beekeeping regions within the state. Research colonies will be established in cooperator apiaries and monitored by the Davis, California, ARS Bee lab scientists. Using a combination of laboratory and field methods, the following parameters will be recorded over the entire duration of the project plan: (1) colony performance parameters including weight, brood and food storage areas, adult bee population, queen laying patterns, honey and pollen storage areas, and prevalence of pests and pathogens including viruses, (2) reproductive performance parameters measured on queens and drones including viability of the sperm in the spermathecae of queens and in the semen of drones and (3) apiary parameters including beekeeper operating costs, their profit margins and available floral resources and their bloom time in the vicinity of the apiaries. To determine the efficacy of automated hive monitoring technologies, inhive sensors will be installed in the experimental hives. Hive performance measures recorded by the automated devices will be compared with the parameters recorded by researchers during the same time periods in the same apiaries. As a part of Sub-objective 1B, the expression of hygienic behavior, an important a form of behavioral resistance to American Foul Brood (AFB) and a behavioral defense against chalkbrood, will be quantified in the colonies of the participating stakeholder apiaries and the impact of nutrition on behavioral expression will be determined using the established Freeze Killed Brood assay. The second objective of the project plan is to determine the effects of nutritional and agrochemical stressors on honey bee health. Towards this goal, field and laboratory studies in Sub-objective 2A will determine the impact of monocrop and multi-floral pollen diets on colony-level performance measures and individual bee-level behavioral parameters. To determine the effects of agrochemical stressors on honey bee reproduction and development, laboratory studies in Sub-objective 2B will explore how Insect Growth Regulators used in almond orchards affect honey bee queen fecundity and the survival and performance of offspring.

Progress Report
This is the final report for project 2030-21000-055-000D, "Conduct Longitudinal Studies on Colony Performance and Explore Near-term Effects of Nutritional and Agrochemical Stressors on Honey Bee Health", which was replaced by new project 2030-30500-001-000D, "Determining Effects of Nutritional and Agrochemical Stressors on Honey Bee Health, via Longitudinal Studies on Colony Performance and Direct Tests". For additional information, see the new project report. Specialty crops such as almonds in California are highly dependent upon honey bees for pollination services. The almond industry has grown exponentially in recent years, increasing the co-dependence between almond as an early food source for the honey bee and their pollination services to produce high quality and increased yields of almonds. ARS researchers in Albany, California, now are aware of the importance of honey bee pollination for almond productivity but have yet to understand how almond pollination affects long-term honey bee colony health and whether cover crops used in conjunction with migratory beekeeping practices can improve colony strength and performance. The results of the long-term monitoring experiments described in Sub-objective 1A show that colonies placed in almond orchards had consistently more frames of bees, pollen stores, brood, and adult bees returning from almond pollination service versus before almond pollination. In addition, the availability of mustard-mix cover crops increased colony strength throughout the season, suggesting that these colonies are more likely to overwinter into the next beekeeping season. Findings suggest that almond pollination is beneficial for honey bee colony strength and performance but cover crops can further increase colony strength by providing a more balanced diet. One peer-reviewed manuscript describing these findings has been published with more in preparation, and these results have been presented at stakeholder conferences and in stakeholder media. Progress was made for subordinate project 2030-21000-055-003S, "Analyzing Factors Contributing to Long-term Honey Bee Health and Hive Performance". Specific phytochemicals that have been shown to have beneficial effects on honey bees are being investigated as supplements to enhance colony performance. Colonies were fed phytochemicals (caffeine, p-coumaric acid, or a mix) at two concentrations (25 ppm and 250 ppm). Colony strength, hygienic behavior, and Varroa infestation were unaffected by treatment. Worker bees reared in situ on 250 ppm p-coumaric acid exhibited a trend toward increased survival in paired cage studies. Additionally, performance of honey bee stocks in California and their responses to stress are being evaluated to identify the best stocks to use under different scenarios. Six bee stocks were compared for Varroa resistance and colony performance over two years. Two stocks clearly showed decreased mite infestation; however, all stocks performed better than expected in suppressing Varroa mites, even without additional treatments. Colony productivity varied by stock and year, influenced by drought and Varroa pressure. Queen failure and overwintering losses were highest in colonies with greater mite burdens and smaller populations. These findings highlight the complex interactions between genetics, environment, and nutrition in shaping honey bee health and emphasize the need for integrated approaches to improve colony resilience. Substantial progress was made on subordinate project 2030-21000-055-015S, "Improving Honey Bee Health and Food Security" through breeding and IPM control of parasitic mites in California. The parasitic mite, Varroa destructor, and the viruses it vectors are considered to be the most concerning threat to honey bees. Experiments have been conducted to evaluate the effects of blocking Varroa efflux pumps on the efficacy of available miticides with the goal of developing miticide synergists. The results have been presented at stakeholder conferences and a manuscript summarizing the results is in review. Additionally, experiments describing the influence of viruses on honey bee queens have been conducted in collaboration with researchers at the University of British Columbia. These experiments demonstrated that viral infections impair queen reproduction and significantly impact the expression of proteins in their eggs, suggesting that viral infections in bee colonies can have transgenerational effects. These findings, which have been described in two published, peer-reviewed manuscripts, underscore the importance of controlling the mites that vector these pathogens. Honey bee hygienic behavior, or the removal of dead or infected brood from a colony, is a heritable trait that confers benefits such as disease resistance to a colony. Efforts to determine whether nutrition impacts the expression of genes related to hygienic behavior described in Sub-objective 1B are nearly complete. Hives of three cooperators were sampled after almond and after sunflower pollination for RNA sequencing, from which ARS scientists can determine how gene expression related to hygienic behavior is affected. Samples were submitted to the University of California, Davis, Genomics Core Facility, but the sequencing data from this effort was deemed to be inadequate to draw meaningful conclusions. However, this work is being continued by collaborators at William Patterson University, who will use samples collected from a similar experiment to relate colony performance to nutrition, and gene expression patterns associated with hygienic behavior. This information will help beekeepers determine the impact of different diets on a beneficial, heritable trait associated with disease resistance in bee colonies. For Sub-objective 2A, experiments aimed to explore the effects of different nutrient conditions on the performance of honey bees. When honey bees are foraging there are two possible learning phenotypes – slow, accurate individual learners and fast, inaccurate social learners. There are costs and benefits of these different learning strategies, and how the neurophysiological mechanisms can be impacted that underlie such cognitive variation remain less understood. The results of experiments comparing learning between groups of honey bees fed different diets suggest that neurotransmitter metabolite precursor derived from a variety of nutrients of a honey bee diet can influence individual and social learning accuracy and speed in different ways, which are likely to have impacts on pollination efficacy. Underlying nutrients from a honey bee diet may increase or decrease the performance of these two different learning strategies depending upon amino acid availability. These findings, which have been published in a peer-reviewed manuscript, will lead to the creation of improved dietary supplements for bees and improved pollination services and crop yields. Beekeepers and growers have a shared interest in ensuring that the agrochemicals used to treat the crops that bees pollinate are safe for honey bees, but limited data is available on how maternal exposure to agrochemicals can influence colony dynamics like reproduction. Under Sub-objective 2B, a comprehensive evaluation of the effects of maternal exposure to the juvenile hormone mimic, pyriproxyfen, on honey bees was completed. Previously, it was reported that pyriproxyfen may positively influence aspects of honey bee reproduction following queen exposure and that it changes the pattern of protein expression in queen ovaries in a manner that is consistent with the positive impacts observed on egg hatching rates. Now, proteomic characterizations have demonstrated that maternal pyriproxyfen exposure has a limited impact on protein expression in newly emerged worker bees. This suggests that maternal pyriproxyfen exposure is not harmful to bees, and experiments are currently being conducted to further explore these positive effects on reproductive behavior in a field level study. Ultimately, this may lead to the development of novel treatments to enhance honey bee reproduction, which will yield more reliable and effective pollination services for farmers and enhanced food security. These results have been communicated to both stakeholders and scientific audiences through presentations, peer reviewed manuscripts, and stakeholder media. Substantial progress was made on subordinate project 2030-21000-055-007S "Quantifying the Effects of Pesticides on Honey Bee Reproduction". Samples collected to expose bees to agrochemicals have been analyzed, and a manuscript describing the chemical residues in relevant maternal and worker tissues is in preparation. Another manuscript describing the expression dynamics of important detoxification genes across different ages and castes of honey bees has been submitted. Broadly, it was determined that immature bees have lower expression of critical efflux receptor genes, which likely relates to lower pesticide tolerance. This information can be used by beekeepers and growers to better protect honey bees from potential negative effects of agrochemicals, thus enhancing pollination and ensuring adequate crop yields for farmers. Taken together, the results generated during the execution of project 2030-21000-055-000D produced insights into the effects of various agricultural practices in the California Central Valley Region on honey bee health and longevity. This region, which provides a large portion of the fruit, nut, and vegetable crops consumed in the United States, is of critical importance on a national scale, and by extension, so are the honey bees that provide farmers with crucial pollination services. This work will provide a baseline understanding of how various practices influence aspects of honey bee performance that can be built upon to generate new tools and mediation strategies to combat the stressors that lead to colony failure.

Accomplishments
1. A hormone mimicking pesticide has no adverse effects on honey bee queens even at high concentrations. Honey bee queen performance is a critical aspect of colony health, and hormone mimicking pesticides used during pollination events have been known to negatively impact aspects of colony reproduction. ARS researchers in Albany, California, collaborated with researchers at the University of British Columbia, to demonstrate that queen exposure to pyriproxyfen, a juvenile hormone mimic used in blooming almond orchards to control pests, does not have any adverse effects on honey bee oviposition rates and colony performance. This information will sustain use of a key insecticide, and will help beekeepers maintain healthy queens, while narrowing the scope of future research required to identify the cause of failing queens.

2. Inhibiting cellular efflux pumps enhances the toxicity of miticides used to kill a devastating honey bee parasite. Varroa destructor mites are widely considered to be the primary cause of honey bee colony loss, but widespread resistance to existent chemical control strategies has made it difficult to control their populations. ARS researchers in Albany, California, collaborating with researchers at the University of California, Davis, determined that Varroa were more susceptible to Amitraz, a widely used miticide, when it was combined with inhibition of cellular efflux pumps, which are responsible for removing toxins from cells. The effectiveness of this approach opens up new lines of research that will result in the development of novel miticide synergists to kill Varroa destructor and enhance the health and pollination performance of honey bees.

U.S. DEPARTMENT OF AGRICULTURE

Invasive Species and Pollinator Health: Albany, CA