Electronic Supplementary Material - Ramirez et al.pdf from Abscisic acid enhances cold tolerance in honeybee larvae

The natural composition of nutrients present in food is a key factor determining the immune function and stress responses in honeybee (<i>Apis mellifera</i>). We previously demonstrated that a supplement of abscisic acid (ABA), a natural component of nectar, pollen and honey, increases honeybee colony survival overwinter. Here we further explored the role of ABA in <i>in vitro</i>-reared larvae exposed to low temperatures. Four-days-old larvae (L4) exposed to 25°C for 3 days showed lower survival rates and delayed development compared to individuals growing at a standard temperature (34°C). Cold-stressed larvae maintained higher levels of ABA for longer than do larvae reared at 34°C, suggesting a biological significance for ABA. Larvae fed with ABA-supplemented diet completely prevent the low survival rate due to cold stress and accelerate the adult emergence. ABA modulates the expression of genes involved in metabolic adjustments and stress responses: <i>Hexamerin 70b, Insulin Receptor Substrate, Vitellogenin</i> and <i>Heat Shock Proteins 70.</i> AmLANCL2, the honeybee ABA receptor, is also regulated by cold stress and ABA. These results support a role for ABA increasing the tolerance of honeybee's larvae to low temperatures through priming effects.