Honey bee forager thoracic temperature inside the nest is tuned to broad-scale differences in recruitment motivation

Abstract

Insects that regulate flight muscle temperatures serve as crucial pollinators in a broad range of ecosystems, in part because they forage over a wide span of temperatures. Honey bees are a classic example and maintain their thoracic muscles at temperatures (T(th)) tuned to the caloric benefits of floral resources. Using infrared thermography, we tested the hypothesis that forager motivation to recruit nestmates for a food source is positively correlated with T(th). We trained bees to a sucrose feeder located 5-100 m from the nest. Recruiting foragers had a significantly higher average T(th) (2.7°C higher) when returning from 2.5 mol l(-1) sucrose (65% w/w) than when returning from 1.0 mol l(-1) sucrose (31% w/w). Foragers exhibited significantly larger thermal fluctuations the longer they spent inside the nest between foraging trips. The difference between maximum and minimum temperatures during a nest visit (T(range)) increased with total duration of the nest visit (0.7°C increase per additional min spent inside the nest). Bees that recruited nestmates (waggle or round danced) were significantly warmer, with a 1.4-1.5 times higher ΔT(th) (difference between T(th) and nest ambient air temperature) than bees who tremble danced or simply walked on the nest floor without recruiting between foraging bouts. However, recruiter T(th) was not correlated with finer-scale measures of motivation: the number of waggle dance circuits or waggle dance return phase duration. These results support the hypothesis that forager T(th) within the nest is correlated to broad-scale differences in foraging motivation.