Temperature Sensing and Honey Bee Colony Strength

Abstract

Strength auditing of European honey bee (Apis mellifera Linnaeus, 1758 [Hymenoptera: Apidae]) colonies is critical for apiarists to manage colony health and meet pollination contracts conditions. Colony strength assessments used during pollination servicing in Australia typically use a frame-top cluster-count (Number of Frames) inspection. Sensing technology has potential to improve auditing processes, and commercial temperature sensors are widely available. We evaluate the use and placement of temperature sensing technology in colony strength assessment and identify key parameters linking temperature to colony strength. Custom-built temperature sensors measured hive temperature across the top of hive brood boxes. A linear mixed-effect model including harmonic sine and cosine curves representing diurnal temperature fluctuations in hives was used to compare Number of Frames with temperature sensor data. There was a significant effect of presence of bees on hive temperature and range: hives without bees recorded a 5.5°C lower mean temperature and greater temperature ranges than hives containing live bees. Hives without bees reach peak temperature earlier than hives with bees, regardless of colony strength. Sensor placement across the width of the hive was identified as an important factor when linking sensor data with colony strength. Data from sensors nearest to the hive geometric center were found to be more closely linked to colony strength. Furthermore, a one unit increase in Number of Frames was significantly associated with a mean temperature increase of 0.36°C. This demonstrates that statistical models that account for diurnal temperature patterns could be used to predict colony strength from temperature sensor data.

Keywords: Apis mellifera; honey bee; pollination; strength; temperature.

Fig. 1.

Number of Frames audit of the beehive used photographic capture of the frame top prior to assessment of the photographic image by two auditors. Hive lids were opened on the west side of north facing hives.

Fig. 2.

Connection diagram of sensor arrays to data logger unit. Six temperature arrays containing four temperature sensors were in each of the six hives in a group, and a single temperature sensor measured external ambient temperature. Data was logged to a MicroSD data storage card which was removed and read at the end of the experimental period.

Fig. 3.

Sensor position across a North facing (upward) Langstroth hive containing nine frames. Sensor numbers run sequentially from outside to center.

Fig. 4.

Temperature range is shown against sensor placement from the center of the hive in hives with bees (active colonies, left) and hives without bees (inactive colonies, right). Shade indicating colony strength. Predicted temperature ranges (linear) are plotted for hives with colonies of a strength of 1.166NOF (dark/blue) and 7NOF (light/yellow), and on the right in hives without bees. The presence of an active bee colony (left) significantly reduced the temperature range measured in the hive compared to those measured in hives without bees (right). Daily temperature range increases significantly with distance from the hive center in all hives, but by less in hives without bees. However, the effect of colony strength (Number of Frames) on observed temperature range is not significant (See online version for color figures).

Fig. 5.

Example of observed data fit to model predictions of temperature. Temperature data from sensor 3 in hive eight (Number of Frames = 2), overlayed on the predicted temperature for sensor 3 in a hive where Number of Frames = 2. Observed datapoints largely fall within the 95% prediction interval.