Location: Invasive Species and Pollinator Health
2024 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 report documents progress for project 2030-21000-055-000D, titled, “Conduct Longitudinal Studies on Colony Performance and Explore Near-term Effects of Nutritional and Agrochemical Stressors on Honey Bee Health”, which started in May 2021.
In support of Sub-objective 1A, ARS researchers in Albany, California, aimed to establish long term honey bee research (LTHBR) sites, and two additional apiary locations for research colonies are now being occupied and used on a regular basis in Woodland and Davis, California. New contacts have been made with stakeholders in northern California for future expansion of the long-term monitoring. All colonies continue to be monitored for their health and performance by recording frames of bees, egg laying, number of adult bees, brood area, amount of pollen, nectar and honey stores, and the amount of Varroa mites in each of the experimental colonies. ARS scientists are now conducting once a month detailed assessments for the entire year while working with three stakeholders. Queens continue to be analyzed once a year and in the most recent year new versus old queen quality is being considered. Preliminary analyses of data collected in Year 1, Year 2, and Year 3 are also underway. Once Year 3 data collection is complete, these three years of data will be analyzed for a publication. A possible treatment for the inactivation of microsporidian spores, known as Vairimorpha ceranae, that may be harbored on beekeeping equipment, which is a pathogen of honey bees, has now been developed for beekeepers. These findings have been published.
For Sub-objective 1B, ARS researchers set out to determine whether nutrition impacts the expression of hygienic behavior and colony performance. Hives of three cooperators have been sampled after almond and after sunflower pollination for RNA sequencing, from which ARS scientists can determine how the gene expression related to hygienic behavior are affected based on previous Quantitative Trait Loci mapping of these gene regions. The RNA sequencing of the samples is now complete and the data has been obtained, this now needs to be analyzed. Scientists have also completed lab experiments to understand the effects of rearing bees on the different pollen diets and how this impacts the survival of adult bees.
In experiment 1 of Sub-objective 2A, ARS scientists investigated forager preference of pollen from different crops grown in California. ARS researchers in Davis, California, compared behavioral preferences of honey bee foragers provided with a choice of mixed cover crop pollen and pollen from almond and sunflower monocrop fields. They observed that foragers prefer pollen from mixed cover crop habitat that includes a variety of different plant species. ARS researchers have compiled behavioral data and nutritional composition of the different pollens used in the choice assay. The mixed species pollen was found to be chemically diverse that was richest in cholesterol, vitamins, and phytochemicals quercetin, kaempferol, coumarin, and quinine. However, the mixed species pollen did not have the highest levels of essential amino acids as well as polyunsaturated fatty acids. The diversity in chemical profiles does not always correlate with higher levels of plant species diversity, but the findings suggest that foragers will still prefer to collect a variety of pollen types when available. The findings also reiterate the importance of providing honey bees with access to diverse floral resources for optimal health. Results of these findings have been accepted for publication.
Experiment 2 of Sub-objective 2A focuses on the impact of monocrop diet and a mixed source pollen diet on behavior in honey bees. ARS researchers have adapted protocol from experiment 1 above to raise adult bees in hives provided with controlled diet - mixed cover crop pollen and pollen from monocrop fields. Assessment of pollen consumption, sucrose consumption, survival, health biomarker gene expression, viral loads, bee weight, learning and memory abilities have now been completed. The data was collected, and a preliminary analysis has been completed. Mechanisms of appetite regulation in forager honey bees have been investigated, and ARS researchers observed that the forager age class, in particular, have pathways that may function independent of the glucose-insulin signaling pathway and this independent pathway may lead to their ability to make rapid adjustments, to adjust their intake levels for obtaining particular nutrients. The understanding of this pathway sheds light on how the honey bee may buffer against energetic stress that can be caused by microsporidian honey bee pathogens. The appetite regulation findings have now been published.
Experiment 2 of Sub-objective 2B involves assessing the negative effects of insect growth disrupting chemicals on queens and their offspring. It was previously reported that the juvenile hormone mimicking insect growth disruptor, pyriproxyfen, positively influenced aspects of honey bee reproduction following queen exposure. Proteomics analysis of eggs and queen ovary tissue has been completed, and results indicate that pyriproxyfen treatment changes the pattern of protein expression in queen ovaries in a manner that is consistent with the positive impacts observed on egg hatching rates. These results, which may lead to the development of novel, beneficial treatments for queen bees, have been published in a peer-reviewed journal. Presentations to both stakeholder and scientific audiences to describe the scientific and applied implications of this work have been scheduled. To further explore potential mechanisms of the observed effects, an experiment exposing queens to juvenile hormone is currently underway.
Progress with sample analyses continues in the subordinate project (2030-21000-055-005S, "Modeling Honey Bee Exposure to Pesticides in Pollination Dependent Crops of California"). DNA metabarcoding to identify plant sources of pollen has been performed and pesticide residue analysis is ongoing. The findings of this subordinate project relate to main project objectives that target long term factors affecting honey bee health in California. Prevalence of pesticides and diversity of pollen sources are two critical long-term factors impacting honey bee colony performance.
Additional progress has been made for the subordinate project (2030-21000-055-003S, "Analyzing Factors Contributing to Long-term Honey Bee Health and Hive Performance"). This includes completing the analysis of a study that focuses on the effects of almond pollination services and planted mustard mix cover crop in almond orchards on colony strength and performance. It was found that almond pollination services aid mainly in the buildup of the colony strength with higher amounts of pollen stores, brood, and adult bees during the early spring months. However, planted mustard mix cover crop resulted in additional positive effects on colony strength and nectar stores for colonies providing almond pollination services and these effects lasted long into the beekeeping season thereby increasing the chances for overwintering survival. It was also found that access to honey bee pollination significantly improves nut set and whole tree yields for the newer self-compatible variety of almonds, ultimately resulting in economically meaningful gains to almond growers. Recently completed caged trials and a field study revealed that the phytochemical p-coumaric acid, when fed as a dietary supplement, extends the life of worker bees, but at a colony level, reduces the amount of brood present in the colony. Another field trial is currently underway to determine if lower queen egg laying is the cause for the reduced brood area in the p-coumaric acid treated colonies. These findings will help inform the management practices of beekeepers and may lead to improved recommendations for improving colony health and longevity. Collectively, these findings were presented at 12 different international and national level beekeeping and academic conferences.
The subordinate project (2030-21000-055-001S, "Analyzing Nutritional Content of Pollen in Relation to Long-term Honey Bee Colony Health") was completed in August 2023. In Experiment 1 of Sub-objective 2A, ARS researchers in Davis, California, showed that honey bee foragers collect pollen from all the choices provided in the arena, with a preference for pollen from the mustard-dominated cover crop mix. This subordinate project demonstrated that pollen from mustard-dominated cover crop mix was chemically diverse and richest in cholesterol, vitamins, and phytochemicals, but not consistently high for essential amino acids and polyunsaturated fatty acids. The analyses also provided detailed information on the nutritional quality of pollen from honey bee hives placed in almond orchards and sunflower fields, two important pollination-dependent monocrops in California. A manuscript describing these findings has been published.
Satisfactory progress has been made on the subordinate project (2030-21000-055-007S, "Quantifying the Effects of Pesticides on Honey bee Reproduction"). Initial experiments to expose bees to agrochemicals have been performed and efforts to develop techniques to evaluate and quantify pesticide residues in relevant tissues are currently underway. These methods will be refined and used to determine the fate and impacts of agrochemicals on honey bee physiology when encountered in various settings. A manuscript describing these approaches has been published.
Accomplishments
1. A novel treatment for inactivating Nosema spores. Vairimorpha (Nosema) is a fungal pathogen that is globally distributed and is implicated as a key disease in the most recent decline of honey bee health. There is no effective treatment on the market for the spore stage of the pathogen and this is the stage in which it is dispersed to further infect other honey bees. Consequently, the spores can potentially contaminate beekeeping equipment. ARS researchers in Albany, California found that a large molecule (Zinc phthalacyonine) treatment was effective within 1 hour at reducing the number of viable Nosema spores and, when used under light conditions, the potency increased with an 80 percent reduction in the number of viable spores. This new treatment compound, with light activation, may be particularly beneficial for treating Nosema spores located on beekeeping equipment, which can help reduce the spread of this pathogen and potentially improve colony health. Using this treatment on live honey bees has yet to be tested but also may be a suitable new treatment option for reducing Nosema infection loads at the colony level.
2. Exposure to trisiloxane surfactant adjuvants negatively affects queen egg laying and increases viral replication in worker honey bees. Trisiloxane surfactants are a commonly used class of pesticide adjuvants used on crops where honey bees forage. An experiment was conducted jointly by ARS researchers in Davis, California, Logan, Utah, and Baton Rouge, Louisiana, and at Utah State University to investigate their effects on honey bees at field relevant doses. This work demonstrated that one trisiloxane variant negatively influenced queen oviposition rates and exposure to another resulted in increased replication of a common honey bee pathogen in honey bee workers. These findings provide insight into the effects of adjuvants on honey bee health and may be used to inform their risk to honey bees.
3. Octopamine regulates honey bee forager appetite independent of the glucose-insulin signaling pathway. To ensure that there is enough energy to carry out life activities, hunger and appetite regulate food intake. How the two communicate and regulate one another remains largely unknown, especially for invertebrates. ARS scientists in Albany, California, found that for forager honey bees there is a connection between blood trehalose levels, two neurotransmitters in the brain, and appetite levels. These changes were independent of insulin production. Their results suggest that forager bees may have an alternative pathway for appetite regulation that is based on the amount of the trehalose sugar found in their hemolymph. In vertebrates, blood glucose acts as the primary sugar indicating what level of hunger an individual should have to maintain energetic balance via the insulin-signaling pathway. However, trehalose levels fluctuate more in the hemolymph of insects and therefore may be a more direct indication of the energetic state of the individual, consequently this newly identified appetite regulation pathway may be responsible for more rapid and efficient way to regulate appetite, which would be necessary for a foraging bee that is constantly undergoing large fluctuations in energetic demanding activities. Understanding mechanisms of appetite regulation can aid in improving beekeeping management practices by preventing energetic stress that may be caused by honey bee diseases and can also lead to ways to more easily monitor energetic stress via physiological biomarkers.
4. Exposure to insect growth disrupting pesticides during development influences the expression of expression of endocrine modulating genes in honey bee worker tissues. Previously, it was demonstrated that honey bee workers reared under exposure to sublethal doses of insect growth disrupting pesticides are less responsive to queen pheromone, which may negatively affect reproduction in a colony setting. ARS researchers in Davis, California, further investigated this phenomenon by evaluating changes in the expression of genes in the brains and hypopharyngeal glands of exposed workers, demonstrating that developmental exposure to insect growth disrupting pesticides impacts endocrine signaling genes in tissues that are critical for provisioning brood and for regulating behaviors in worker honey bees. These findings provide insight into the effects of pesticides on honey bee health and may be used to inform the risk of insect growth disrupting pesticides to honey bees.