Correlative light- and scanning electron microscope studies on the developmental morphology of Hesperomyces virescens

Abstract

The morphological development of Hesperomyces virescens (Laboulbeniales) parasitic on the ladybird beetles Adalia bipunctata and Olla v-nigrum [Coleoptera, Coccinellidae] was studied by correlative light (LM) and scanning electron microscopy (SEM). The bicellular ascospores are frequently discharged in pairs, and these elongate on contact with the integument of the host. Initial adhesion appears to rely on the inflated portion of the sheath surrounding the tip of the larger of the two ascospore cells. This tip subsequently swells and forms the main organelle of attachment, the melanized foot. The larger ascospore cell elongates, divides and forms the three-celled receptacle and the perithecium. The smaller cell produces the antheridial appendage. Removal of developing foot cells from the host surface revealed a small (ca. 1μm) circular penetration hole and evidence of remnants of an adhesive gasket-like “O-ring”. A relatively extensive, branched, nonseptate rhizoidal haustorial apparatus was also observed. An elaborately lobed trichogyne is produced which is in close proximity to mature antheridia of the same individual. The perithecial apical apparatus is complex and unique, probably acting as a contact trigger for ascospore release. These morphological observations strongly support the importance of self-fertilization as the primary reproductive strategy in this fungus.

Key Words:

• adhesion
• ascospore
• development
• Laboulbeniales
• melanin