Systematics and biology of two species of Microcera associated with armoured scales on citrus in Australia

Microcera coccophila has been regarded as an entomopathogen of armoured scales in Australia since the late 1800s. We confirmed its identity and presence in Australia using morphological and molecular data. We also confirmed that a related species, M. larvarum, is an entomopathogen of armoured scales in Australia. M. coccophila was recorded as a parasite of Aonidiella aurantii, A. citrina, Lepidosaphes beckii, L. gloverii and Unaspis citri in citrus orchards on the Central Coast of New South Wales. We recorded M. larvarum in these orchards in association with A. aurantii and one or more hosts that could not be identified due to their condition. The sexual and asexual morphs of both species are described. Genetic variation suggested that the taxa could represent various phylogenetic species. We fulfilled Koch’s postulates for both fungi in separate bioassays with Aspidiotus nerii. Infection was not dependent on the reproductive status of the scale. A laboratory study showed that Iridomyrmex rufoniger, a common ant in Australian citrus orchards, can passively disperse conidia of M. coccophila. Field observations suggested that the prevalence of the two fungal parasites in orchards is influenced by host scale densities, climate, and foraging by I. rufoniger workers on honeydew produced by their sternorrhynchan trophobionts, particularly Saissetia oleae. These foraging activities induced dense populations of A. aurantii by disrupting the activities of the scale’s natural arthropod enemies; this was followed by epizootics of M. coccophila that decimated populations of the scale.