Location: Invasive Species and Pollinator Health
2022 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
For Sub-objective 1A aimed at establishing long-term honey bee research sites, colonies continue to be monitored for their health and performance by recording frames of bees, egg laying, colony growth and other health parameters in each of the experimental colonies. These efforts will continue through the year, adding to the long-term data being collected. Queens were analyzed for total number of sperm in spermatheca, percent sperm viability and percent spermatheca filled, which together yield insemination and overall grades for each queen. Temperature monitoring sensors are being adjusted to improve recording precision and the data reporting frequencies continue to be calibrated to better integrate with the recording done by researchers.
For Sub-objective 1B that aims to determine whether nutrition impacts the expression of hygienic behavior within honey bee hives, we have identified the apiary where experiments will be conducted, and hives with treatment diets are set up. For evaluating hygienic behavior as affected by nutrition, we have begun standardizing the protocols used for testing.
Experiment 1 of Sub-objective 2A aims to determine 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 monocrop fields. Scientists observed that foragers prefer pollen from mixed cover crop habitat that includes a variety of different plant species. Scientists continue to extract data from the video recordings of forager choice of pollen diets. The observed behavioral patterns will be combined with data from the video recordings to make a final determination of forager choice. The pollen used for the choice tests is being analyzed for nutritional composition, which will allow the scientists to explain the nutritional basis for preference.
Experiment 2 of Sub-objective 2B was completed, which focused on characterizing the behavioral effects of embryonic exposure to insect growth disruptors (IGDs). Based on the results of Experiment 1, scientists conducted a follow-up experiment to examine the effects of substantially lower doses of IGDs on honey bee embryos following maternal exposure. Behavioral data were collected on queens and workers under IGD exposure, embryos reared to adulthood using foster colonies, and collected behavioral data on the resultant adult insects and their interactions with new queens. By working with a collaborating lab, scientists analyzed the ovarian protein composition of exposed honey bees, correlating observed behavioral changes in the offspring of IGD exposed queens with changes in protein expression in the queens’ ovary tissues. The findings suggest a possible hormetic effect of an insect hormone mimic resulting in improved responsiveness to honey bee queens. This work was not scheduled to begin until FY2023, but thanks to an international collaboration, scientists are ahead of schedule.
Significant progress was made on a subordinate project (2030-21000-055-005S, Modeling Honey Bee Exposure to Pesticides in Pollination Dependent Crops of California) by exploring how diversity in cropping influences pesticide use in California’s Central Valley. By using mathematical and statistical models to test for consistent differences in the relationship between pesticide use and diversity of crops grown, this study shows a reduced pesticide use in diverse landscapes with a variety of different crops, both in terms of frequency and intensity of application. This study and its findings directly relate to project objectives to improved agricultural practices relevant to honey bee health in California.
Progress on a subordinate project (2030-21000-055-003S, Analyzing Factors Contributing to Long-term Honey Bee Health and Hive Performance) includes recording performance metrics for colonies placed in areas prone to wildfires in California. Scientists have successfully obtained data on the pathology of worker bees from colonies infected by Nosema spp. Samples have been collected to determine expression of stress genes from colonies likely to experience wildfires and to characterize and quantify the Nosema infection. Results of this study will provide baseline data for scientists to compare the effects of wildfires on honeybees.
Progress was made on a subordinate project (2030-21000-055-001S, Analyzing Nutritional Content of Pollen in Relation to Long-term Honey Bee Colony Health). Metabolomic analysis of pollen samples for nutrient composition has been completed and data analysis has begun. These data, when collected and analyzed, are expected to improve understanding of changes in nutritional quality as beehives are moved from almonds to other crops and wildflower habitats in California. The information will allow beekeepers to adjust or supplement nutrition to enhance colony health and performance and improve survivorship throughout the season.
Accomplishments
1. Honey bee foragers exhibit behavioral responses that improve diversity in hive diet. Pollination services provided by honey bees ensure profitable yields in fruits, nuts and vegetable crops commercially grown in California. Beehives placed in fields and orchards for pollination limit bees to a monoculture diet. ARS researchers in Davis, California, have shown that honey bees exhibit distinct behavioral responses that result in improving dietary diversity within hives. Results indicate that, independent of prior foraging experience, honey bee foragers prefer to collect pollen significantly more often from a mixed pollen source, such as that from a pollinator habitat. Along with information on pollen nutritional content, the results of this study provide evidence for foraging preferences by honey bees. In addition, the findings emphasize the need for wildflower plantings alongside monoculture crop fields to provide honey bees a source of mixed pollen. This information educates producers of the importance of bee-friendly habitats for sustaining healthy pollinator populations.
2. Developmental exposure to hormone mimicking insect growth disruptors (IGD) alters the responsiveness of adult worker bees to queen pheromone. Honey bee pollinators may be exposed to IGD pesticides while foraging and they can accumulate in wax and pollen. ARS researchers in Davis, California, have demonstrated that exposing worker larvae to IGDs causes reduced interest in queen pheromone. In young workers, queen care behavior is elicited in response to queen-produced pheromones, and if queens do not have enough attendants responding to them, they will not be as productive. These results provide evidence that exposure to hormone mimicking IGDs during development can affect important behaviors that may contribute to decreased colony expansion. Understanding how developmental IGD exposure can influence the behavior of workers enables the development of management recommendations to improve the long-term stability of honey bee colonies.
Review Publications
Litsey, E.M., Chung, S., Fine, J.D. 2021. The behavioral toxicity of insect growth disruptors on Apis mellifera queen care. Frontiers in Ecology and Evolution. 9. Article 729208. https://doi.org/10.3389/fevo.2021.729208.
Fine, J.D., Litsey, E.M. 2022. Drone laying honey bee workers in queen monitoring cages. Journal of Insect Science. 22(3). Article 13. https://doi.org/10.1093/jisesa/ieac021.
Geldert, C., Abdo, Z., Stewart, J., Seshadri, A.H. 2021. Dietary supplementation with phytochemicals improves diversity and abundance of honey bee gut microbiota. Journal of Applied Microbiology. 130(5):1705-1720. https://doi.org/10.1111/jam.14897.
Seshadri, A.H., Hardin, J. 2021. Pollinator-friendly flora in rangelands following control of cheatgrass (Bromus tectorum): A case study. Invasive Plant Science and Management. 14(4):270-277. https://doi.org/10.1017/inp.2021.33.
