DOI: 10.5061/dryad.5tb2rbpg5
title: Negative effects of excessive heat on colony thermoregulation and population dynamics in honey bees

description: Insect pollinators, including honey bees (Apis mellifera), are essential
 for agriculture and terrestrial ecosystem function, yet their responses to
 warming conditions and heat waves remain poorly understood. Honey bees
 have well-documented mechanisms to cope with heat exposure that could help
 them adapt to extreme heat. However, there have been no studies to date
 that have assessed how natural heat waves affect the capacity of honey bee
 colonies to thermoregulate and grow. To test the hypothesis that excessive
 heat impairs honey bee colony growth by exceeding the thermoregulatory
 capacity, we studied how variation in summer temperatures affected hive
 temperature regulation and colony growth during a desert summer in which
 maximal shaded air temperatures intermittently exceeded 40°C. We monitored
 the growth of nine colonies biweekly for three months and recorded
 temperatures at the center and edge frames of the brood nest, as well as
 on combs at the outer edge of the hive body.  Average
 temperatures in the brood center and edge were quite stable and within the
 optimal range of 34-36°C necessary for healthy brood development
 throughout the summer.  However, all hive locations exhibited
 cyclic, diurnal thermal fluctuations, and brood experienced considerable
 portions of each day (14% for the brood center, 33% for the brood edge)
 above and below the optimal temperature range. Higher maximal air
 temperatures and greater temperature fluctuations within the hive led to
 declines in colony population. These findings suggest that excessive heat,
 with maximal temperatures exceeding 40°C, can reduce colony populations by
 impairing the thermoregulation of brood or by exposing adults to
 temperatures that shorten their lifespans. If excessive heat periods occur
 more frequently as predicted due to climate change, this could limit
 regions where colonies can successfully survive the summer.
description: <strong>Colony establishment and
 maintenance</strong> From May to August 2022,
 nine colonies of Apis mellifera ligustica were monitored at the Arizona
 State University Polytechnic campus. Before the experiment commenced, each
 colony was provided with a new queen (in April 2022), sourced from Pendell
 Apiaries Inc. in Stonyford, CA (39.376956, -122.558801). Initial colony
 sizes varied from 3,000 to 13,000 bees, with four double-box hives and
 five single-box hives. <strong>Colony population
 assessments</strong> The response of the colonies
 to climatic conditions was monitored through regular assessments of their
 growth and development.  We inspected every hive biweekly to estimate the
 number of adult worker bees and brood levels across all life stages from
 May 18th, 2022, to August 22nd, 2022. We took two sets of photographs of
 each side of every frame using a Canon® EOS Rebel T5 camera. The first
 set, taken with adult bees still on the frame, was analyzed using ImageJ
 (National Institutes of Health) to estimate the number of adult workers
 through “Multi-point” counting (Fisher II et al., 2022). For the second
 set, we gently shook and brushed the bees off the frame and placed a 877.2
 cm² grid over the comb to measure how many cm² were occupied by the pupae.
 If a grid cell wasn’t completely filled, we calculated a fraction based on
 the number of filled cells out of 23 (the average number of cells in our
 grid cells of 6.45 cm²). Because eggs and larvae were difficult to detect
 in the photographs, an observer estimated their total abundance in the
 field by counting the number of grids and cells occupied by eggs or larvae
 within the 877.2 cm² grid. <strong>Temperature
 Logging</strong> Temperature was monitored in the
 hives at 6-minute intervals from May 18th to June 13th and at 30-minute
 intervals from June 14th to August 22nd using Telid® RFID temperature
 loggers (Microsensys, Erfurt, DE).  Each hive box was equipped with five
 loggers. Two loggers were positioned near the edges of the peripheral end
 frames, which were generally partially or completely filled with food
 reserves (usually honey) and lacked brood.  Three additional loggers were
 allocated to the brood frames, including one in the brood's center
 and two at the brood area's edge for each box. The locations of the
 loggers were adjusted during the population surveys, if necessary, to
 maintain their positions relative to the brood. The temperature data were
 extracted using a Telid® RFID sensor and software (Microsensys, Erfurt,
 DE). Phoenix-Mesa Gateway Airport (Mesa, AZ: 33.307833,
 -111.655472) is located approximately 1.5 miles from the ASU honey bee
 laboratory, and its temperature readings serve as our source for shaded
 air environmental data. The data were obtained from the MesoWest website
 (https://mesowest.utah.edu/), developed by the University of Utah. Temperature is recorded every 20 minutes from 0 to 5 am; for the remaining time in a day, temperature is recorded hourly. Daily variability of temperatures in the hives was assessed through the diurnal temperature range (maximum minus minimum recorded for that day). All loggers were analyzed by logger positions: Outer Edge (OE), Brood Edge (BE), and Brood Center (BC). To examine the relationship between temperature and colony population size variation, we calculated the average diurnal thermal range over two weeks for temperature loggers, as well as the two-week averages of daily maximum and minimum temperatures. Additionally, to assess the amount of time that bees experienced potentially stressful temperatures, we calculated the duration brood spent at temperatures outside of the optimal thermal range of 34- 36 °C.
description: # Negative effects of excessive heat on colony thermoregulation and
 population dynamics in honey bees Dataset DOI:
 [10.5061/dryad.5tb2rbpg5](10.5061/dryad.5tb2rbpg5) ## Description of the
 data and file structure This study examined the impact of extreme summer
 temperatures on honey bee colony thermoregulation and population dynamics.
 **1. Overview** This collection of datasets was compiled to investigate
 how excessive heat exposures influence honey bee colony population
 dynamics. The data includes in-hive temperature records, shaded air
 temperature data, and demographic assessments of colonies. **2. Data
 Sources** • In-hive temperature data were recorded using loggers at
 various locations within the hive, including the Brood Center (BC), Brood
 Edge (BE), and Outer Edge (OE). • Shaded air temperature data were
 obtained from the nearby airport’s temperature recordings. • Demographic
 data were collected biweekly and included the populations of adults,
 pupae, larvae, and eggs. **3. Dataset Summaries** • bc.csv: Brood center
 temperature data. Time format is: Month/Date/Year, Hour: Minutes. •
 be.csv: Brood edge temperature data. Time format is: Month/Date/Year,
 Hour: Minutes. • oe.csv: Outer edge temperature data. Time format is:
 Month/Date/Year, Hour: Minutes. • BC_summer.csv: Brood center temperature
 data. Time format is Month/Date/Year. • BE_summer.csv: Brood edge
 temperature data. Time format is Month/Date/Year. • OE_summer.csv: Outer
 edge temperature data. Time format is Month/Date/Year. •
 Temperature_Differences_All_by_logger.csv: This dataset contains daily
 temperature summaries (maximum, minimum, mean, and temperature difference)
 recorded by individual loggers installed at three hive positions: Brood
 Center, Brood Edge, and Outer Edge. • airport_summer.csv: Daily airport
 temperature readings aligned with demography dates. • summer_data.csv: all
 in-hive temperature data together aligned with demography dates. •
 pop_change_noZero.csv: Colony population change data with zero-change
 entries removed. • pop.csv: colony population data. **Variables** bc.csv,
 BC_summer.csv, be.csv, BE_summer.csv, oe.csv, OE_summer.csv,
 summer_data.csv, airport_summer.csv and population_(Fig3).xlsx  1. Time or
 Date: Timestamp of the temperature recorded measurement.  2. F:
 Temperature recorded in degrees Fahrenheit (°F). 3. Temperature:
 Temperature recorded in degrees Celsius (°C). 4. Session: Logger recording
 session. 5. Hive: Numeric identifier for the hive.  6. LoggerID: Numeric
 identifier for the temperature logger. 7. Loggercode: Position of the
 logger within the hive (Brood center, Brood Edge, and Outer edge). 8. Box:
 Location of the logger in the hive box. Upper / Lower for double-box
 hives. Single for single-box hives. 9. Demography.Date or Demography: Date
 of colony population assessment. 10. Time_diff: Time interval between two
 logger recordings. Temperature_Differences_All_by_logger.csv: 1. Date or
 Time: Timestamp of the temperature recorded measurement.  2. Hive: Numeric
 identifier for the hive. 3. Logger: Numeric identifier for the temperature
 logger. 4. Position: Position of the logger within the hive (Brood center,
 Brood Edge, and Outer edge). 5. Demography: Date of colony population
 assessment. 6. Max: Daily maximum temperature. 7. Min: Daily minimum
 temperature. 8. Mean: Daily average temperature. 9.
 Diff: Daily temperature differences (daily maximum - daily minimum).
 pop.csv: 1. Colony.ID: Numeric identifier for the hive. 2.
 demography: Date of colony population assessment. 3. Adults: Population of
 adults. 4. Pupae: Population of pupae. 5. Larvae: Population of larvae. 6.
 Eggs: Population of eggs. 7. Total: total population of adults, pupae,
 larvae, and eggs together.  pop_change_noZero.csv: 1. Colony.ID: Numeric
 identifier for the hive. 2. demography: Date of colony population
 assessment. 3. Adults: Population change of adults between two demographic
 dates. 4. Pupae: Population change of pupae between two demographic dates.
 5. Larvae: Population change of larvae between two demographic dates. 6.
 Eggs: Population change of eggs between two demographic dates.
 population_(Fig3).xlsx * Date: The time interval when samples were
 collected (about 14 days each). * Eggs, Larvae, Pupae, Adults: These are
 the average (or total) numbers counted for each life stage during that
 period. * std.egg, std.larvae, std.pupae, std.adults: These are the
 standard deviations, which measure how much the counts varied between
 samples within that same time period. ## Code/software All data were
 analyzed using RStudio. The provided R script files contain the full code
 used for data processing, statistical analysis, and figure generation.
 Note that the scripts do not include `install.packages()` commands; users
 should ensure that all required packages are installed prior to running
 the code. Each code file is named to indicate the specific figure and
 corresponding statistical analysis it supports in the manuscript. **4.
 Contact** For questions about these datasets, please contact Jun Chen
 ([jchen152@asu.edu](mailto:jchen152@asu.edu)). **Access information**
 Other publicly accessible locations of the data: * None Data was derived
 from the following sources: * None