A new but still unpublished entomopathogenic fungus (ARSEF13372) in the genus Pandora (Entomophthorales: Entomophthoraceae) was originally isolated from Cacopsylla sp. (Hemiptera: Psyllidae). Several species of the genus Cacopsylla vector phloem-borne bacteria of the genus ‘Candidatus Phytoplasma‘, which cause diseases in fruit crops such as apple proliferation, pear decline and European stone fruit yellows. To determine Pandora's host range and biocontrol potential we conducted laboratory infection bioassays; Hemipteran phloem-feeding insects were exposed to conidia actively discharged from in vitro produced mycelial mats of standardized area. We documented the pathogenicity of Pandora sp. nov. to species of the insect families Psyllidae and Triozidae, namely Cacopsylla pyri L., C. pyricola (Foerster), C. picta (Foerster, 1848), C. pruni (Scopoli), C. peregrina (Foerster), and Trioza apicalis Foerster. The occurrence of postmortem signs of infection on cadavers within 10 days post inoculation proved that Pandora sp. nov. was infective to the tested insect species under laboratory conditions and significantly reduced mean survival time for C. pyri (summer form and nymph), C. pyricola, C. picta, C. pruni, C. peregrina and T. apicalis. Assessing a potential interaction between phytoplasma, fungus and insect host revealed that phytoplasma infection (‘Candidatus Phytoplasma mali’) of the vector C. picta and/or its host plant apple Malus domestica Borkh. did not significantly impact the survival of C. picta after Pandora sp. nov. infection. The results from infection bioassays were discussed in relation to Pandora sp. nov. host range and its suitability as biocontrol agent in integrated pest management strategies of psyllid pests, including vector species, in orchards.