Apidologie 24 (1993) 383-390
DOI: 10.1051/apido:19930404

Enzymatic equipment of Ascosphaera apis and the development of infection by this fungus in Apis mellifera

J.M. Alonso^a, J. Rey^a, F. Puerta^b, J. Hermoso de Mendoza^a, M. Hermoso de Mendoza^a and J.M. Flores<sup>b

a</sup>  Departamento de Medicina y Sanidad Animal, Facultad de Veterinaria de Cáceres, Universidad de Extremadura 1007/1 Cáceres
^b  Departamento de Ciencias Morfológicas, Sección de Biología Aplicada, Facultad de Veterinaria, Universidad de Córdoba, 14005 Córdoba, Spain

Abstract - The process of infection of honey bee brood by the fungus Ascosphaera apis was initiated by feeding 3rd instar larvae with a known dose of spores. These larvae were extracted from their sealed cells at 2 different times during early postcapping development and processed for SEM. This study was complemented with an analysis of the enzymatic equipment of the fungus, to investigate the mechanism of penetration of the larval cuticle. This analysis was conducted on mycelium isolated from mummies produced in 47 field outbreaks of chalkbrood and on 3 reference strains. There was evidence of enzymes such as N-acetyl-β-glucosaminidase in 74.4% of the isolates, which can break down the molecules of N-acetyl-glucosamine. Chitin, the main component of the cuticle, is a polymer composed of these molecules. This enzyme, assisted by a certain pressure from the hyphae, as these fungal elements are generated inside the larval body, may explain how the fungus pierces the cuticle.

Key words: Ascosphaera apis / Apis mellifera / larval cuticle / penetration / infection / enzyme