2026 ABRC Proceedings

Part 1

https://doi.org/10.55406/ABRC.4.26.1

The American Association of Professional Apiculturists (AAPA) is an organization consisting of professors, state apiarists, scientists and students who all study and work with the western honey bee, Apis mellifera. The goals of the AAPA apply to three major areas: 1) promoting communication within and between industry, academia, and the beekeeping community; 2) developing and fostering research on fundamental and applied questions to gain a greater understanding of bee biology in an aim to assist and improve the beekeeping industry; and 3) creating a venue to rapidly share new techniques and current research to advance the field.

One way AAPA fulfills its core mission is by hosting the American Bee Research Conference (ABRC) annually. ABRC is a venue for sharing scientific research, and the conference promotes communication, collaboration within and between industry, academia and the beekeeping community.

ABRC 2026 took place in Mobile, Alabama in conjunction with the American Beekeeping Federation’s (ABF) annual meeting. Drs. Jay Evans (USDA-ARS) and Dewey Caron (University of Delaware) delivered keynote addresses titled, “Honey bee colony losses: Causes and consequences” and “Citizen science key participants in master beekeeper/bee atlas programs,” respectively. Over the course of the conference, 68 other presentations were given by members of various academic, industrial, and governmental research institutions on a diverse range of topics including honey bee behavior, physiology, management, nutrition, pathogens, parasites, and extension. Approximately half of all presenters were students, many of whom participated in the student competition. The winners of the 2026 competitions were Ben DeMoras (Auburn University), Kaylin Kleckner (University of Florida), Jennifer Standley (Auburn University), Sarah Jendresky (Arizona State University), and Fernanda Noemi Gonzalez (University of Southern Mississippi).

In our efforts to share the latest research with the beekeeping community, AAPA is delighted to publish the abstracts from this year’s ABRC in Bee Culture. The published abstracts from the conference proceedings have been split into two parts: Part 1 contains topics relating to behavior, nutrition, pathogens, and pesticides, while Part 2 contains topics regarding physiology, varroa, extension, and management and breeding. Thanks for reading and for participating in this year’s ABRC.

The editors of the 2026 ABRC Proceedings:
Edward Hsieh1,2 and Elizabeth M. Walsh1

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1USDA-ARS, Honey Bee Breeding, Genetics, and Physiology Research, Baton Rouge, LA, USA
2ORISE-ORAU, US DOE, ARS Research Participation Program, Oak Ridge, TN, USA

Topic: Behavior

Catch My Drift: Patterns and Effects of Drifting on Pest and Pathogen Transmission within Apiaries
Oral presentation
Coleman CH, Street GM, Walsh EM
The honey bee (Apis mellifera) is the most prominent insect pollinator and is facing a global increase in over-wintering colony losses. Pests and pathogens are considered by many the strongest drivers of colony decline in North America, but knowledge gaps in transmission between hives impede alleviating these stressors. One method of pest and pathogen transmission in honey bee colonies is through “drifting,” when an individual bee returns to a foreign colony and is accepted. This behavior can have a detrimental effect on the hive, particularly via the transmission of Varroa destructor mites or Nosema spp. spores potentially leading to colony death without management intervention. Past drifting research, although foundational, has been limited by reliance of human observation. The application of popular computer vision techniques can gain new insight into honey bee drifting to better understand the relationships between drifting, pest and pathogen transmission, and overall colony health. Here, I implement a video monitoring system leveraging automated computer vision to identify individually marked bees and observe their movements between hives. I quantify pest and pathogen loads, measure colony health metrics, and analyze the relationship between individual bee movement and the spread of pests and pathogens in a controlled apiary.

Heritability and ecological consequences of individual variation in honey bee waggle dance communication
Oral presentation
Couvillon MJ, Schürch R, Johnson LE, Ohlinger BD, McHenry LC
In the honey bee waggle dance, a successful forager recruits nestmates by communicating the distance and direction to high-quality resources. Distance is encoded in the duration of the waggle run. Interestingly, the dance is startlingly inefficiency, with a high rate of failure: only c. 25% of recruits succeed in finding advertised resources, perhaps due to variation in the durations that individual dancers express, a phenomenon that we term “individual calibrations”. Here we set out to test if calibration similarity, where a dancer and a recruit possess similar calibrations, might support successful recruitment. Surprisingly and contrary to our expectations, we instead found that calibration differences, in particular where a dancer “dances long” for a given distance compared to her eventual recruit, actually represents a majority of successful dance recruitment events. We conclude that individual differences in calibration can impact communication and may even confer adaptive benefits, shaping emergent outcomes like colony-level exploitation of resources. Additionally, these data reshape our understanding of honey bee communication, or more appropriately, miscommunication. Future research should investigate what may give rise to these individual calibrations between bees.

Focusing attention toward food-related odors in the honey bee, Apis mellifera: A comparison of methods
Oral presentation
Dixon K, Smith BH
Latent Inhibition (LI) is a form of learning in which a neutral stimulus, to which animals show little response prior to conditioning, is presented over a series of trials without any consequence (reinforcement). It is an important way of focusing attention toward potentially meaningful stimuli. Later conditioning of this now ‘familiar’ stimulus is slowed, possibly because of reduced attention to that stimulus. Latent Inhibition has been widely studied in vertebrates and has recently been identified in insects such as the honey bee, Apis mellifera, using Proboscis extension reflex (PER) conditioning protocols. Our objective was to compare two methods to evaluate behavioral processes which will be important for any field application. After initial exposure to odor – 40 discreet or 1 hour constant – we conditioned bees to two odors, the now familiar odor and a different ‘novel’ odor. We further tested for evidence of physiological differences between bees exposed to these different protocols. We did not observe differences, leaving open reasons for behavioral differences. The resulting differences of these techniques have implications for enhancing honey bee foraging success.

Investigating differing daily foraging patterns in bee-attractive flowers
Oral presentation
Hearon LH, Johnson RM
While the timing of pollinator foraging has been well studied at large phenological scales, within-day dynamics are less represented in the literature. This is likely due to the prohibitively intensive sampling required to observe daily patterns with sufficient resolution. We conducted a diverse pollinator monitoring project using a bioacoustic method that detects the buzz of insect flight with a resolution of ~1 second, providing continuous observation with extreme temporal resolution. Recorders were deployed opportunistically near bee-attractive flowers, yielding recordings from 23 types of flower and just under 11,000 hours of data. Audio data were analyzed with “buzzdetect”, our lab’s free and open-source pollinator monitoring tool. The results show strongly differing patterns of pollinator activity between flowers. The total number of detections spanned two orders of magnitude, the time of peak foraging varied by plant from 7:00am to 6:00pm, and the breadth of foraging activity varied considerably. We hypothesize that these patterns are driven by underlying differences in the timing of floral resource production. These results inform our basic understanding of plant-pollinator interactions and bee foraging behavior and hold applied implications such as the choice of seed mixes for bee-friendly plantings and the timing of pesticide application.

Flight duration is predictive of distance flown for bees foraging on artificial feeders, but not for freely foraging, waggle-dancing bees
Oral presentation
Johnson LE, Schürch R, López-Uribe MM, Shaw TJ, Underwood RM, Couvillon MJ
Organic beekeepers must provide their honeybees with a large area of synthetic pesticide-free/reduced land, even though most foraging trips occur at short distances. Current methods of estimating bee flight ranges, including decoded waggle dances, are unsuitable to estimate foraging ranges on organic farms. Using flight duration to estimate distance has potential, but this method is untested. Here we tested the viability of this new method first by observing the flight durations of individually marked bees foraging at known distances to form a calibration. Then we used this calibration to estimate distance from flight duration for freely flying, recruiting bees, which we then compared to the same bees’ waggle dance distance estimate. We found that flight duration had a significant, positive relationship with distance flown for bees visiting feeders. Our calibration produced significantly accurate, albeit imprecise, distance predictions for feeder-foraging bees. However, we found that a freely foraging bee’s flight duration is inversely proportional to her waggle run duration, which is positively related to distance. This inverse relationship is perhaps because the use of dancers nonrandomized the sample of foragers. Overall, flight duration may be cautiously used to estimate distance, as predictions will often reflect a maximum distance per duration.

Modeling the influence of environmental features on wild honey bee colony density in South Africa
Oral presentation
Kleckner K, Mdiza W, Hill M, Campbell L, Ellis JD
While the western honey bee (Apis mellifera) is well studied as managed livestock, relatively little is known about unmanaged populations of this important pollinator. Across Africa, the ecology of wild honey bees remains understudied. Geographic Information Systems (GIS) provide powerful tools to explore environmental features relevant to colony establishment and survival. We aimed to identify environmental features influencing wild honey bee populations in the Eastern Cape Province, South Africa. We surveyed 1 km2 grids for wild honey bee colonies using beelining techniques, with which we followed foragers from stands with sugar water to their nest entrances. We used colony density data (colonies/km2) alongside environmental predictor variables to construct generalized linear mixed effect models and perform model selection. We explored vegetation type, water availability, and topography as environmental predictor variables using satellite imagery and digital elevation models. In total, we surveyed 16 km2 across five field sites and located 105 colonies. Colony density ranged from 0 to 14 colonies per km2. Our research associated the spatial distribution of environmental features with wild colony density across spatial scales. To conserve honey bees, the complex interactions between colonies and their environments must be understood.

How does stored food impact honey bee foraging behavior in carrot seed?
Oral presentation
Reed R, Hopkins BK
Foraging honey bees transferring pollen between fields is a substantial concern for producers of carrot (Daucus carota) seed and other insect pollinated seed crops. In this study, we tested the influence of colony food reserves and empty space on the foraging behavior of honey bees during carrot seed pollination. Colonies were manipulated to create a range of conditions from colonies with depleted food reserves and abundant empty space to colonies with abundant reserves and little to no empty space. Pollen traps, entrance activity monitors, and observation hives were used to monitor pollen collection, foraging activity, and forage locations via waggle dances, respectively. The results of this study showed that manipulating the food reserves of a colony can significantly alter its foraging behavior.

Examining chronic dimethoate toxicity and diet consumption patterns of Apis mellifera (L.) in group – vs individually-caged laboratory bioassays
Oral presentation
Zuber J, Schmehl D, Haas J, Schneider D, Hamilton A, Ahmad Z, Dolezal A
Regulatory agencies require a standardized set of honey bee laboratory data to assess the risk of pesticides to pollinators. Chronic adult toxicity is often evaluated following the Organization for Economic Cooperation and Development (OECD) guideline #245 which requires groups of ten bees to be housed in each cage and provisioned with spiked sugar solution from a single feeder. Diet consumption is measured to determine the average daily dose per bee, yet there is uncertainty on the assumption that the diet is consumed equally amongst the group-housed bees. The objectives of this study are to determine whether group-caged honey bees result in a different toxicity threshold (e.g., LD50 value) than individually-caged honey bees, and whether feeding patterns are different when bees may exhibit food exchange through trophallaxis. Our results demonstrate that individually-caged honey bees exhibit a highly variable, pulsed, consumption of diet, often including days of minimal to no measurable feeding. A more homogenous daily diet consumption pattern was observed in the OECD 245 design, yet average daily consumption and LD50 toxicity values were not statistically different across the group-caged and individually-caged test design. These results inform predictive model development (e.g., BeeGUTS) and the regulatory suitability of current study designs.

Topic: Nutrition

Examining the pollen and nectar nutritional quality and quantity of nine canola varieties for pollinators
Oral presentation
Becher J, Chakrabarti P
Large-acreage monoculture crops, such as canola, utilize honey bee pollination commercially. However, honey bees have access to only one major pollen and nectar variety in monocultures as their forage source during these pollination contracts. Having access to optimal nutrition is important for colony health. This is why it is crucial to understand the nutritional quality of pollen and nectar of different varieties of crops, such as canola, to assess the nutritional impacts of monocropping systems on honey bee colonies. My project aims to gain insight into the nutritional differences between canola varieties to benefit both beekeepers and growers during a canola pollination event. In the Summer of 2025, nine canola varieties were examined for their nutritional differences. We tested pollens for quantity, protein and lipid quality via established methods, and tested nectars for quantities and sugar percentages.

Nano-B-feed Enhances Pollination Efficacy and Boosts Total Fruit Yield in Almond and Apple Orchards
Poster presentation
Eshed Y, Ackerman-Lavert M, Eshed A, Stern R
Honey bee pollination is essential for almond and apple production, yet environmental stressors and pesticide exposure often diminish colony performance during bloom. In this study, we evaluated the impact of Nano-B-feed, a hive nanoscale-based supplement, on bee activity, fruit set, total yield, fruit size, fruit weight, seed count, and colony resilience across commercial almond orchards (Um-el-fehem) and apple orchards (Granny Smith, Pink Lady, and Gala). Nano-B-feed increased bee vitality and enhanced foraging activity. Colony activity at the hive entrance was significantly increased by at least 30% and more bees were counted on the orchard trees. In almonds, treatment improved fruit set by 28% and increased total yield by 34% compared with untreated controls. In apples, it increased average crop weight by 24% and boosted individual fruit weight by an average of 8.5%. Treated colonies exhibited reduced mortality and demonstrated stronger recovery following two pesticide-related exposure events. These findings indicate that Nano-B-feed enhances pollination efficiency, strengthens colony resilience, and significantly improves orchard yield and overall profitability.

Using clover in agriculture to improve bee forage and increase soybean yield
Oral presentation
Johnson L, Johnson R
The corn-soybean crop rotation system is widespread in the Midwest agricultural landscape. In this system, honey bees and soybeans have a mutually beneficial relationship where nectar is provided in exchange for pollination that can improve yield. However, honey bees living in this system do not have access to a variety of food sources, leaving them nutritionally limited. At the same time, growers frequently manage low-yielding field areas that cost more to farm than they return. Planting clover patches in low-yielding areas of fields represent a potential “win-win solution” for bees and growers. The implementation of clover could provide bees with a supplemental food source. At the same time, clovers planted in the field remove low-yielding areas from production, benefiting growers. This experiment investigates the potential for clover within soybean fields to increase bee activity and soybean yield. To assess this, honey bee activity was measured at various distances from clover patches using audio recordings processed through a machine learning model trained to detect bee buzzing. Soybean yield was measured through hand-harvesting. Together, these data will test the viability of in-field clover patches as a strategy to enhance bee forage while reducing production costs and potentially increasing yields for soybean growers.

Topic: Pathogens

Interaction of pollinators: Sharing pathogens and impacts of viruses and Vairimorpha on honey bees, bumble bees, and solitary bees
Oral presentation
Cox-Foster DL
The sharing of pathogens among bee species is of interest since honey bees are perceived by some to have negative impacts on other non-Apis species. This talk will present the results of studies that asked how viral pathogens impact honey bees, bumble bees, and Osmia species, using longitudinal studies and in vitro rearing studies. In addition, data will be presented on the lack of infection by Varimorpha ceranae in Osmia lignaria, with evidence that other microsporidia related to V. ceranae are naturally existing in wild populations.

Understanding European foulbrood disease epidemiology in honey bees
Oral presentation
Hobday M, Shrestha A, VanLeuven J, Chakrabarti Basu P
European foulbrood (EFB) is a bacterial honey bee infection caused by the bacteria Melissococcus plutonius. This disease affects larvae and prevents them from emerging as healthy adults. Beekeeper anecdote suggests that symptomatic EFB is becoming increasingly problematic following blueberry pollination, and researchers have yet to pinpoint the causative factors of this disease. Through a series of laboratory assays, we will expose honey bee larvae to various stressors to identify what leads to higher larval susceptibility to this disease. Using our findings, we will generate mitigative measures to benefit beekeepers and growers.

Variable susceptibility to chalkbrood infection between Russian honey bee lines and life stages
Oral presentation
Hsieh E, Simone-Finstrom M, Walsh EM
Ascosphaera apis is the fungal species that causes chalkbrood, common honey bee brood pathogen capable of reducing colony populations and draining overall resources. Although preventative measures can be taken, no marketable treatment currently exists to cure an infected colony. This deficit has driven interest in the development of cultural controls such as genetically resistant honey bee lines. Russian honey bees (RHB) are naturally varroa-resistant, but less is known about their resistance to bee diseases. To measure RHB genetic contributions, I repeatedly exposed multiple colonies of 11 RHB lines to aerosolized chalkbrood spores and quantified the resultant infected larvae for two-week periods. After identifying the most and least susceptible colonies, I then in vitro reared larvae from the corresponding colonies and orally inoculated them with A. apis to separate colony phenotypes from larval resistances. Although initial findings indicate certain lines and colonies are more susceptible to chalkbrood than others, high levels of variation within lines and across infection rounds suggest that additional factors such as seasonality or nutrition may also significantly influence chalkbrood resistance. Subsequent testing and methodological refinement will contribute toward the development of a chalkbrood IPM program, ultimately leading to improved sustainability of the apicultural and agricultural industries.

Comparing the dynamics of Black queen cell virus infection between developing workers and queens
Oral presentation
Kaufman CNG, Rueppell O
Virulence, or the death and damage caused to diseased hosts by a pathogen, is poorly understood for honey bee viruses. This is particularly true for Black queen cell virus (BQCV), which typically is asymptomatic in adults and developing workers, but can discolor and kill developing honey bee queens. To understand the conditional virulence and to eventually develop BQCV management strategies, we must first investigate the patterns of BQCV infection in queens and workers over time. Thus, we surveyed developing queens and workers inoculated with BQCV for mortality and virus titre during the critical developmental period. As predicted, experimental BQCV inoculation decreased the survival of developing queens, while the survival of same-aged workers was unaffected. Viral copy numbers after inoculation exhibited complex temporal dynamics in both castes, with a singular distinguishing data point suggesting further research is needed to unravel the puzzle of BQCV virulence.

Regulation of microRNA Expression Dynamics by Acute Bee Paralysis Virus in the Honey Bee (Apis mellifera) Cell Line AmE-711
Poster presentation
Kumar D, Goblirsch M, Adamczyk J, Karim S
Honey bees (Apis mellifera) are essential pollinators for global food security, yet their populations are increasingly threatened by habitat loss, pesticides, parasites, and pathogens. Viral infections represent a major concern, particularly when amplified by the parasitic mite Varroa destructor, a vector of multiple bee viruses. Understanding how bees respond at the molecular level is therefore critical for colony health. MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression in both hosts and viruses, remain an understudied component of antiviral defense. In this study, we investigated miRNA responses in honeybee-derived AmE-711 cells following exposure to Acute Bee Paralysis Virus (ABPV). We compared uninfected cells with cells infected by ABPV, treated with heat-killed virus, or exposed to a viral mimic. Sequencing revealed 481 miRNAs, with 15 significantly altered by ABPV infection. These results suggest miRNAs may contribute to host defense or viral manipulation, providing new insights into honey bee health.

Screening antifungal compounds for inhibitory action against hyphal growth and spores of Ascosphaera apis, the causative agent of chalkbrood
Oral presentation
Masnjak A, Hsieh E, Simone-Finstrom M, Walsh L, Jack C
The genus Ascosphaera comprises spore-cyst–forming fungi found exclusively in association with bees. While most species are harmless saprophytes, Ascosphaera apis is an entomopathogen and the causative agent of chalkbrood disease in the honey bee (Apis mellifera). There are currently no effective treatments for chalkbrood, and its presence adds to the growing stressors faced by managed colonies. Recent surveys indicate substantial annual colony losses, driven by pests, pathogens, pesticide exposure, and nutritional stress, underscoring the importance of studying pathogens such as A. apis. Here, we evaluated the inhibitory activity of five antifungal compounds — propiconazole, chlorothalonil, benzimidazole, iprodione, and thymol — against A. apis using a modified Kirby–Bauer assay. Three compounds demonstrated inhibitory action: chlorothalonil, iprodione, and propiconazole. Among them, propiconazole exhibited the strongest antifungal activity, whereas chlorothalonil showed the weakest effect. The concentration of chlorothalonil needed to inhibit A. apis would likely be toxic to bees. Future work will assess the safety of these compounds for adult and larval honey bees reared in vitro and develop safe, field-ready application strategies. Such efforts will help determine whether chalkbrood infections can be reduced efficiently and practically for beekeepers.

Understanding the dose-dependent effect of Nosema ceranae Infection on Honey Bee innate immune system
Oral presentation
Oeth M, Kumar D, Alburaki M, Golblirish M, Karim S
Nosema ceranae is a pathogenic microsporidian that infects honey bees (Apis mellifera), weakening immunity, and contributing to colony decline. This study examined how varying doses of Nosema infection impact the bee innate immune system and survivability. Bees were divided into four groups: three treatment groups inoculated with varying Nosema spore suspensions (103, 105, & 107), and a control group fed only sugar syrup (1:1). Three-day old bees were inoculated with Nosema spores or with syrup ad libitum. Nosema infection was quantified using a qRT-PCR assay 15 days post Nosema inoculation to quantify the infection in the infected bees. Bee survivability, syrup consumption, hemolymph volume, and hemocyte population counts were assessed on day 1, 2, 4, 7, 11, and 15 post-infection. Mortality increased with spore dose, with the highest dose (10⁷) reducing survival to 64%. Hemolymph volume was reduced by ~2µL in 105 and 107 groups compared to the controls. Granulocyte, plasmatocyte, and prohemocyte populations were most affected, with significant reductions in 105 and 107 groups. These results demonstrate a dose-dependent link between Nosema infection and physiological decline, highlighting the value of monitoring spore loads to inform colony management and reduce losses.

Temporal and spatial distributions of pathogens in managed Florida honey bee (Apis mellifera) colonies
Oral presentation
St. Amant J, Ellis JD, Jack, CJ
Western honey bee (Apis mellifera) pathogens are a major concern for beekeepers and pose a significant threat to colony health. From January – December 2024, adult honey bees were sampled monthly by beekeepers in twenty counties distributed around Florida. Honey bees from each colony sample were analyzed using PCR and microscopy to determine the temporal and spatial distribution of the following honey bee pathogens: Ascosphaera apis (causative agent of chalkbrood), Crithidia mellificae, Melissococcus plutonius (causative agent of European foulbrood), Malpighamoeba mellificae, Lotmaria passim, Nosema apis, and Nosema ceranae. In total, 721 samples were collected, of which 4.3% were positive for A. apis, 65.2% were positive for L. passim, 25.3% were positive for M. plutonius, 84.6% were positive for N. ceranae, and <0.01% were positive for M. mellificae. Crithidia mellificae and N. apis were not detected in any of the samples. There were significant differences in the presence of L. passim, M. plutonius, N. ceranae, and N. ceranae infection levels based on the time of year and location of the colony, with pathogens trending towards higher abundance in summer. Overall, honey bee pathogens in Florida need further monitoring, especially the pathogens that negatively impact honey bee health.

Effects of Gut Homogenate Transfaunation on Nosema ceranae Infection in Honey Bees
Poster presentation
Tiwari S, Palmer J, Huang W-F, Webster TC
Nosema ceranae, a microsporidian parasite damages the midgut epithelium and disrupts digestive and immune function of honey bees. This study tested whether native gut microbiota transfaunation i.e.feeding newly emerged bees a homogenate prepared from healthy adult midguts, could improve resilience against N. ceranae. A total of 1,600 bees were assigned to four groups (control, Nosema only, gut homogenate only, and gut homogenate + Nosema) and monitored for 15 days. Histological evaluations at 6, 9, 12, and 15 dpi showed that gut-homogenate–treated bees had better epithelial integrity, reduced peritrophic membrane separation, and lower cell sloughing (p < 0.05), even under high pathogen loads. 16S rRNA sequencing was used to assess microbial transfer. Microbiomes across treatments displayed comparable alpha diversity and were dominated by typical honey bee gut phyla like Proteobacteria, Firmicutes, Actinobacteriota, and Bacteroidota as well as core genera such as Gilliamella, Snodgrassella, Lactobacillus (Firm-4/Firm-5), and Bifidobacterium. Because transfaunation did not substantially shift microbial diversity, the protective effects may also involve bioactive proteins or other midgut-derived components. A follow-up experiment using heat-treated gut homogenate is underway to separate microbial from non-microbial mechanisms. Overall, gut homogenate transfaunation appears to be a promising, low-cost approach for supporting midgut integrity during N. ceranae infection.

Topic: Pesticides

Investigating “inert” ingredients and insecticidal soap for Varroa mite control
Poster presentation
Johnson RM, Shannon B, Richard S, Foster A
Varroa mites are a major cause of honey bee colony loss. As mites are becoming resistant to common miticides, new treatments are needed. Inert ingredients and surfactants that have potential as either new miticides or as formulation components for other active ingredients. We tested the inert ingredients cyclohexanone, 1-butanol, xylene, methyl isobutyl ketone, BC12, L-7500, AE-13, SE-11, and insecticidal soap, as a positive control, for their efficacy against Varroa mites using a vial bioassay. Varroa mites were obtained by using a sugar shake on bees collected from colonies with high mite levels. Compounds were coated on the interior of 20-mL glass scintillation vials to which five mites were added along with a honey bee pupa. Mite mortality was assessed after four hours. Concentration-response curves were created in order to find the median lethal concentration for each compound. Additionally, cage assays were performed with a dilution series using the most promising compound tested, insecticidal soap. Mite drops and dead bees were counted at 24 and 48 hours after setup. After 48 hours, mites were removed from the bees with an alcohol wash, and all bees and mites were counted. Concentration-response curves were generated for both mites and bees.

The effects of a mitotoxic fungicide on honey bee (Apis mellifera) queen reproduction and worker health
Oral presentation
Fisher II A, Chen J, Harrison J
Honey bees are an integral part of agricultural systems all over the world. Though their economic and environmental contributions remain crucial, they are increasingly threatened by various environmental stressors. Agrochemical application, including fungicide use, aid in the protection of crops from pests and pathogens but adversely affect honey bee health and colony survival. To investigate the effects of a fungicide on honey bee reproduction and health, we tested the hypothesis that exposure to field relevant fungicide concentrations negatively affects honey bee queen egg laying rates and worker health. A non-treated control group was compared to three treatment groups consisting of various concentrations of Luna® Sensation fungicide (a.i.: fluopyram, trifloxystrobin). Our findings indicated that Luna® Sensation reduced egg laying rates at the highest concentration tested. Additionally moderate to high fungicide concentrations altered hypopharyngeal gland acini. These findings suggest that fungicide consumption adversely affects honey bee queen reproductive competence and worker health which may reduce colony population levels.

Did pesticide exposure play a role in the record 2024-2025 colony losses?
Oral presentation
Sanchez AB, Anderson WB, McArt SH, Chen YP, Evans JD, Lamas ZS
High overwinter colony losses in 2024-2025 prompted USDA scientists to conduct emergency sampling in January 2025 immediately prior to almond pollination. Here, we describe contamination of sampled colonies from six commercial beekeeping operations that experienced high overwinter losses. Bees, pollen (bee bread), and wax from colonies that were weak, medium-strength, or strong were screened for 95 pesticides via LCMS. We found high pesticide contamination in all matrices, with bees, pollen, and wax containing an average of two, four, and seventeen pesticides, respectively. No differences in contamination were observed among weak, medium-strength, or strong colonies. All matrices contained fungicides, herbicides, and insecticides, but amitraz breakdown products (2,4-DMPF and 2,4-Dimethylaniline) were the dominant residues across all matrices, accounting for 94% of residues by mass. Amitraz breakdown product levels in bees represented the highest-risk contaminants, but corresponded to only ~0.5% of a honey bee LD50, representing low acute risk to bees. Assuming varroa mites experienced similar levels of contamination, amitraz breakdown products would correspond to ~25-50% of a mite LD50, representing probable selection pressure for mites to evolve resistance to amitraz. Indeed, resistance to amitraz was observed in 100% of mites tested in the January 2025 sampling of these six operations.

Evaluating differences in honey bee worker age susceptibility to insecticides using thiamethoxam
Oral presentation
Namin SM, Chakrabarti Basu P, Lucas H, Breece C, Topitzhofer E, Sagili R
Honey bees (Apis mellifera L.) are vital pollinators that support global biodiversity and food production, yet colony losses continue to rise due to multiple stressors, including pesticide exposure. Although regulatory agencies such as the U.S. Environmental Protection Agency have expanded pollinator risk assessment frameworks, Tier 1 laboratory tests still rely almost exclusively on newly emerged workers, overlooking the physiological and behavioral diversity of different age cohorts within the colony. This presents a critical gap, as honey bee workers transition from in-hive nursing tasks to energetically demanding foraging activities, potentially altering their susceptibility to pesticides. In this study, we investigated the age-dependent responses of newly emerged bees, nurse bees, and foragers exposed to field-relevant concentrations of thiamethoxam under controlled laboratory conditions. Survival analysis revealed cohort-specific differences: foragers exhibited the highest mortality, nurse bees showed intermediate sensitivity, and newly emerged bees were least affected. Behavioral assays demonstrated that foragers consumed more sugar syrup and water, resulting in higher pesticide intake relative to body size, while thiamethoxam exposure stimulated increased water consumption across all age groups, suggesting a compensatory detoxification response. Measurements of oxidative stress (ROS/RNS) further indicated that pesticide exposure accelerated stress accumulation, particularly in foragers, with levels initially elevated and then declining over time, pointing to potential physiological adaptation. These findings highlight the importance of considering the differences in survival and physiology of different age cohort of honey bees in the current pesticide risk assessments.

Microbial biopesticides are inhibited by the in vitro diet used in larval honey bee laboratory bioassays
Oral presentation
Schmehl DR, Larsen D, Gomez C, and Ortego LS
Royal jelly is a substance secreted by the hypopharyngeal glands of worker honey bees and is the primary component of the in vitro honey bee larval diet according to the OECD 239 test guidance. Royal jelly is a complex and nutrient-rich substance yet has several bioactive properties that may create barriers for the testing of microbial-based plant protection products. While establishing the safety of these materials is as important as for conventional chemicals, there are important distinctions between them. For example, microbes must be evaluated for their pathogenic potential because some microbes are known to only affect the larval stage of bees (e.g., Paenibacillus larvae, American Foul Brood). For characterizing microbial inhibition from in vitro larval diet, five microbes were grown on agar plates and the in vitro larval bee diet was spotted on the plates. Inhibition tests revealed that the diet inhibited the growth of some of the bacteria and fungi, including the known bee pathogen Paenibacillus larvae. This work highlights the need for considering adaptations to current standardized approaches, which may include prework to confirm whether the test material is inhibited when integrated into the royal jelly-based in vitro larval diet.

References
Edward Hsieh & Walsh E M. 2026. ABRC 2026 Proceedings: Part 1. Bee Culture April 2026, Volume 154, Issue 4, pp. 40-46. https://doi.org/10.55406/ABRC.4.26.1