Resistance to american foulbrood in honey bees VIII. Effects of injecting Bacillus larvae spores into adults

Abstract

The pathological consequences of artificially introducing Bacillus larvae spores into the hemolymph of adult bees were investigated by injecting the spores into the thorax of worker bees with a 30-gauge needle and microsyringe apparatus. Viable spore doses ranged from 1.5 × 10 2 to 1.04 × 10 6 per bee. A majority of the spore-injected adults died in less than 61 hr, whereas most water-injected bees lived 142 hr or longer. A statistical analysis of longevity data demonstrated not only a significant difference between spore- and water-injected groups but also that the pathogen reduced the life span in three genetic stocks of bees to an equal level even though stock differences in longevity exist. Following dissection of the dead bees, single vegetative rods and long chains of rods were observed in spore-inoculated bees, thus demonstrating not only spore germination but also bacterial multiplication in the hemolymph. Water-injected bees remained pathogen-free. When spores were injected into the abdominal hemolymph above the dorsal diaphragm, vegetative rods were observed in samples of thoracic hemolymph. Cells of this pathogen were transported via the circulatory system of adult bees from one region of the body to another. Both abdominal and thoracic injections of B. larvae spores produced a general septicemic type disease in adult bees. Endospores were observed in the hemolymph of only one adult bee out of 115 bees given thoracic and abdominal injections of spores.