Annual Differences in Honey Bee Foraging Conditions in Northwest Washington | Whatcom Ag Monthly

Volume 11 Issue 9

By Kayla Brouwer and Lisa DeVetter (WSU Small Fruit Horticulture)

La Niña conditions made things interesting for northwest Washington agriculture. Temperatures during May 2022 were cooler and wetter than average for Whatcom and Skagit counties, where blueberry production is concentrated. These conditions are attributed to colder surface waters in the eastern Pacific Ocean, otherwise known as La Niña. While the full effect of these conditions on crops is being elucidated, we can calculate the number of optimal and marginal foraging hours for honey bees during the blueberry pollination period in May and compare them to previous years where pollination was optimal.

Optimal foraging conditions for honey bees includes sunny-to-partly skies, air temperatures above 60°F, low wind, and dry foliage (Westphal et al., 2008; Vaissiére et al., 2011). Suboptimal conditions for honey bee foraging includes overcast skies, temperatures at or below 60°F, and high wind.

Using weather data collected by AgWeatherNet stations throughout Whatcom and Skagit counties, the number of optimal foraging hours was calculated for 2022 and compared to 2021 in which conditions were generally considered optimal. Note, honey bee foraging tends to increase between 10 am to 4 pm. Skagit County had 147 optimal foraging hours in 2021 and 66 optimal foraging hours in 2022 (Figure 1). Whatcom County had 179 optimal foraging hours in 2021 and 66 optimal foraging hours in 2022. Rainfall was not included in determining optimal foraging hours in this report. However, in May 2021 there were approximately 42 hours that had recorded rainfall for both regions, compared to 100 hours that had recorded rainfall for May 2022. During 2021, only 5 hours were recorded to have rainfall between 10 am and 4 pm (i.e., peak foraging hours). For 2022, 48 hours of recorded rainfall took place between the peak foraging hours of 10 am and 4 pm.

**Figure 1.** Summary of optimal honey bee foraging hours in May 2021 and 2022 using 60 °F as our temperature threshold. Data are from Washington State University AgWeatherNet stations in northwest Washington, USA.

Honey bee foraging has been observed in Washington by our team at temperatures at or above 55°F, so we also calculated the number of foraging hours for each county above a 55°F temperature threshold. These hours were combined with the number of optimal foraging hours mentioned above to calculate the total number of hours honey bees were capable of foraging in northwest Washington. Skagit County had 303 foraging hours in 2021 and 205 hours in 2022 (Figure 2). Whatcom county had 340 foraging hours in 2021 and 210 in 2022 .

**Figure 2.** Summary of total hours of honey bee foraging in May 2021 and 2022 using 55 °F as our temperature threshold. Data are from Washington State University AgWeatherNet stations in northwest Washington, USA.

Figure 3 shows temperature conditions in 2021 and 2022 for northwest Washington (Whatcom and Skagit counties combined) at our 55 and 60 °F thresholds. Figures 4 and 5 show these data specifically for Skagit and Whatcom counties, respectively. The full effects of our marginal pollination season in 2022 will be better understood through yield, berry size, and seed set assessments which are ongoing in the Small Fruit Horticulture lab. Results will be shared at future conferences. Furthermore, detailed knowledge on optimal foraging conditions for honey bees is lacking and will be produced through a collaborative grant project with Washington State University, Michigan State University, Oregon State University, and the University of Florida.

**Figure 3**. Air temperature data for May 2021 and 2022 in northwest Washington (Whatcom and Skagit counties combined). Air temperature threshold lines are shown for 55 and 60 °F (marginal and optimal foraging, respectively), above which indicate hours where honey bees are likely foraging. Data are from Washington State University AgWeatherNet.

**Figure 4.** Air temperature data for May 2021 and 2022 in Skagit County, Washington. Air temperature threshold lines are shown for 55 and 60 °F (marginal and optimal foraging, respectively), above which indicate hours where honey bees are likely foraging. Data are from Washington State University AgWeatherNet.

**Figure 5.** Air temperature data for May 2021 and 2022 in Whatcom County, Washington. Air temperature threshold lines are shown for 55 and 60 °F (marginal and optimal foraging, respectively), above which indicate hours where honey bees are likely foraging. Data are from Washington State University AgWeatherNet.

Want to learn more on blueberry pollination? Check out our project website (https://blueberrypollination.org/) or follow-us on Twitter (@BeesNBerries).

Funding was provided by:

USDA NIFA SCRI Proposal #: 2020-02627
Washington Blueberry Commission

Sources

Vaissière, B., Freitas, B. M., & Gemmill-Herren, B. (2011). Protocol to detect and assess pollination deficits in crops: A handbook for its use (pp. 81-p). FAO.

Westphal, C., Bommarco, R., Carré, G., Lamborn, E., Morison, N., Petanidou, T., … & Steffan-Dewenter, I. (2008). Measuring bee diversity in different European habitats and biogeographical regions. Ecological monographs, 78(4), 653-671.