| Summary: | The Asian citrus psyllid <i>Diaphorina citri</i> Kuwayama (Hemiptera: Liviidae) is the most widespread and devastating pest species in citrus orchards and is the natural vector of the phloem-limited bacterium that causes Huanglongbing (HLB) disease. Thus, reducing the population of <i>D. citri</i> is an important means to prevent the spread of HLB disease. Due to the long-term use of chemical control, biological control has become the most promising strategy. In this study, a novel highly pathogenic fungal strain was isolated from naturally infected cadavers of adult <i>D. citri</i>. The species was identified as <i>Aspergillus fijiensis</i> using morphological identification and phylogenetic analysis and assigned the strain name GDIZM-1. Tests to detect aflatoxin B<sub>1</sub> demonstrated that <i>A. fijiensis</i> GDIZM-1 is a non-aflatoxin B<sub>1</sub> producer. The pathogenicity of the strain against <i>D. citri</i> was determined under laboratory and greenhouse conditions. The results of the laboratory study indicated that nymphs from the 1st to 5th instar and adults of <i>D. citri</i> were infected by <i>A. fijiensis</i> GDIZM-1. The mortality of nymphs and adults of <i>D. citri</i> caused by infection with <i>A. fijiensis</i> increased with the concentration of the conidial suspension and exposure time, and the median lethal concentration (LC<sub>50</sub>) and median lethal time (LT<sub>50</sub>) values gradually decreased. The mortality of <i>D. citri</i> for all instars was higher than 70%, with high pathogenicity at the 7th day post treatment with 1 × 10<sup>8</sup> conidia/mL. The results of the greenhouse pathogenicity tests showed that the survival of <i>D. citri</i> adults was 3.33% on the 14th day post-treatment with 1 × 10<sup>8</sup> conidia/mL, which was significantly lower than that after treatment with the <i>Metarhizium anisopliae</i> GDIZMMa-3 strain and sterile water. The results of the present study revealed that the isolate of <i>A. fijiensis</i> GDIZM-1 was effective against <i>D. citri</i> and it provides a basis for the development of a new microbial pesticide against <i>D. citri</i> after validation of these results in the field.
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