4.4.1. Freezing

Freezing on-site is the gold standard for sample transport, but usually too expensive for mass surveys. There are several alternatives for different purposes and samples sizes (see the BEEBOOK paper on molecular techniques; Evans et al., 2013), including the ‘dry shipper’ which can hold up to 1300 2-ml cryo-tubes below freezing for up to 3 weeks and is approved for international air-shipment.