Cold temperatures can temporarily immobilise adult honey bees by reducing the amplitude of neuron action potentials (Wieser, 1973). Similar to carbon dioxide, length of exposure and dose, as well as recovery time (Frost et al., 2011), can greatly influence phenotypic response to chilling exposure. For example, chilling for 3 minutes at -20 °C did not affect worker longevity, orientation, or foraging behaviour (Ebadi et al., 1980); whereas, ice-chilling at 0 °C for the minimum amount of time needed to immobilise individuals significantly impaired learning, but not sugar responsiveness, compared to refrigeration at 4-5 °C or freezing at -18 °C (Frost et al., 2011). Additionally, honey bee age can influence response to chilling, as newly emerged individuals less than 18 hours old normally move at 22 °C compared to 17 °C for older foragers (Allen, 1959), and 85 % of one day old workers died when exposed for 3 minutes to -20 °C (Robinson and Visscher, 1984) when no death in older workers receiving the same dose was observed (Ebadi et al., 1980).
An exposure of the bee to -20 °C for 3 minutes is recommended to immobilise mature individuals greater than 1 day old using chilling. At this time no recommendation can be made for chilling time of individuals younger than this due to seemingly adverse effects.
Protocol to immobilise honey bees with chilling:
- Place required number of honey bees in a cage.
- Transfer the cage into a freezer (-20°C).
- Remove the cage with the immobilised bees from the freezer after 3 minutes.