Climate change poses significant threats to bumble bee populations, with rising temperatures potentially exceeding critical thermal thresholds for larval development. While adult workers can tolerate temperatures up to 52°C, brood mortality occurs at just 36°C, making nest thermoregulation crucial for colony survival. This study investigated how nest depth affects temperature regulation and colony performance in the common eastern bumble bee (Bombus impatiens).
Ten experimental colonies were established at Blandy Experimental Farm, with five placed at surface level and five buried at 60 cm depth. Temperature data loggers monitored nest and brood temperatures hourly, while trail cameras recorded worker behavior including fanning and incubating activities. RFID tags tracked individual foraging patterns, and brood cell counts assessed colony productivity over a six-week period.
Results demonstrated that deep colonies maintained significantly more stable temperatures, averaging 27.86°C compared to 30.34°C in surface nests. Deep colonies spent 62.4% of time within optimal brood temperature ranges (28-32°C) and never required fanning behavior, while surface colonies spent 38.9% of time above optimal temperatures requiring active cooling. Deep nests produced significantly more brood cells (48.47 ± 2.48) compared to surface nests (26.9 ± 1.09). Structural equation modeling revealed that surface nests closely tracked ambient temperatures, while deep nests were effectively buffered against temperature fluctuations.
These findings suggest that nest depth provides critical thermal refugia for bumble bee colonies under warming conditions, with implications for efforts targeting pollinator resilience to climate change.
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