American foulbrood is a disease that produces effects at colony level, but does not affect the physiological parameters on nurse bees (Apis mellifera)

L.B. GENDE ; P.M. GARRIDO ; N. DAMIANI; N.J. FERNÁNDEZ; M.P. PORRINI ; M.P. MOLINÉ; B.S. ALVAREZ; F. BUFFA; I. FLORIS; M.S. CHURIO ; M.J. EGUARAS

Barcelona

Congreso; VI international conference on environmental industrial and applied microbiology; 2015

Biomicroworld

Paenibacillus larvae is a Gram-positive spore-forming bacterium, and the causative agent of American foulbrood(AFB), one of the most serious and destructive brood diseases of honeybees Apis mellifera. Only sporesrepresent the infectious stage when the larvae have ingested them. A colony is known to be diseased when larvaeare observed with the clinical symptoms; meanwhile, adult honeybees are not affected by P. larvae becomingasymptomatic carriers. At colony level, behavioral mechanisms are involved in disease resistance. The defensesystem used by eusocial insects against pathogens includes changes on individual physiological parameters aswell as group defenses. The aim of this work was to study the spread of P. larvae spores in experimental minihivesand evaluate the impact of higher microbial loads on different physiological parameters of individualworker bees and colony development. After the artificial infection, the experimental design allowed to follow thedevelopment of the disease via the visual inspection. The spores load in the inoculated group was greater than inthe uninoculated one, proving the effectiveness of the inoculation method. In the colonies that showed all clinicalsymptoms of AFB, the average number of spores per bee was significantly higher than 2,855.9 units. Bees thatemerged from one healthy colony were marked and introduced in colonies with severe clinical symptoms ofAFB, as well as on control group. No changes were observed in physiological and immunological defensemechanisms at individual level on marked bees recaptured at 10 days-old when comparing uninoculated andinoculated hives groups. The high sporulate load did not change the total proteins content in hemolymph, thedegree of development of their hypopharyngeal glands and their abdominal fat body by comparison with beesintroduced into uninfected colonies within each analyzed time interval. Nurse bees from the same cohort werenot able to indicate the progressive bacterial infection by altering physiological and immunological parametersstudied. This work constitutes the first study linking the effects of AFB disease with a possible disruption ofnormal development of adult bees under field conditions.