Pathogenicity of Cordyceps javanica (Hypocreales: Cordycipitaceae) to Diaphorina citri (Hemiptera: Liviidae) Adults, with Ultrastructural Observations on the Fungal Infection Process

Abstract

Entomopathogenic fungi are proposed biological control agents against the Asian citrus psyllid (Diaphorina citri). We quantified the pathogenicity of Cordyceps javanica strain Apopka 97 strain (Cja Apopka 97) (blastospores and conidia) against D. citri using the spray technique. We also used light and scanning electron microscopy to observe the Cja Apopka 97, infection process against D. citri adults at different stages pre- and post-mortem. Our findings demonstrated that psyllid mortality in the blastospore treatment ranged from 8 to 25% within 24–48 h of exposure, compared to 0% in the conidial and control treatments. However, psyllid mortality rate had reached 100% by 7 days after exposure at a concentration of 107 spores/mL, under both fungal treatments compared to the controls (0%). SEM and light microscopy revealed several stages in in the Cja Apopka 97 infection process of D. citri, including spore adherence and germ tube formation within 24 h post-inoculation, penetration pegs and mycelia growth on wings after 72 h, rupturing of cuticle after 96 h and mycelial mass colonizing host body after 144 h. Our study findings provide basic information on the interaction of entomopathogenic fungi with D. citri which will assist in the understanding of the infection process and the potential roles of entomopathogenic fungi in its management.