Resistance to American foulbrood in honey bees: VI. Spore germination in larvae of different ages

Abstract

Germination varied when a constant dosage of Bacillus larvae spores was put into the larval food of honey-bee larvae ( Apis mellifera) of different ages. Larvae were fed spores at 3, 21, and 45 hours of age. Samples of larvae were taken and fixed in Carnoy's at 13, 16 1 2 –17 , 19, 22–22 1 2 , and 25 hours after spore feeding. Larval gut contents were smeared on slides and stained with carbol fuchsin, nigrosin, and methylene blue. Vegetative rods were counted under oil immersion in approximately 1% of the fields of the smear. A higher percentage of young spore-fed larvae showed vegetative stages than did the intermediate or older larvae following approximately the same elapsed time for spore germination. Larvae were sampled and fixed at 7 hours after spore-feeding to compare time of ingestion of the spores in the differentaged larvae. Spores were found in a higher percentage of intermediate and older larvae than in younger larvae.