Electropositive redox state of the fifth-instar larval gut of Apis mellifera

A platinum and calomel electrode combination was used to determine the in vivo redox potential (E_h) of the blind-ending midgut of pathogen-free 5th-instar honeybee larvae. In a sample of 20 larvae the mean E_h at 0, 5 and 10 min after electrode insertion was 147 ± 79, 134 ± 44 and 156 ± 56 mV, respectively. The pH of the gut contents was 7.5. The results suggest that anaerobic conditions do not exist in the honeybee midgut, and thus that anaerobiosis is not the stimulus which causes ascospores of the chalk brood fungus Ascosplzaera apis to germinate at this site. It is suggested that an alternative stimulus or an alternative route of entry for the fungus should be considered.