SummaryThe effects of environmental temperature and pH on 3 stages of spore germination inAscosphaera apiswere investigated. Activation and enlargement were independent of temperature within a range of 10 to 40°C, and 25 to 40°C, respectively. Germ-tube production was closely temperature-related, only occurring within the range 25 to 37°C, with an optimum between 31 and 35°C. All 3 stages were independent of pH within the range of pH 5 to 7·8 (equivalent to those found in larval haemolymph and gut contents). Lower pH's (equivalent to those found in honey, pollen, and brood food) drastically reduce enlargement and germ-tube production.A. apisappears to be a pathogen highly specialised for life in honeybee larvae.