Diaphorina citri Kuwayama (Hemiptera: Liviidae), the Asian citrus psyllid (ACP), is the primary vector of huanglongbing, a devastating citrus disease. Hirsutella citriformis, an entomopathogenic fungus (EPF), has shown promise as a biocontrol agent against ACP. Naturally occurring infections have been reported in South and Central Florida, and previous studies confirm ACP’s high susceptibility to H. citriformis. This study surveyed citrus groves in South and Central Florida for natural H. citriformis infections. We evaluated the fungus’s transmission dynamics and efficacy under laboratory and field conditions using 2- to 5-day-old lab-reared ACP adults. In the lab, infected ACP were brushed against healthy individuals to allow direct contact. Experiments were conducted in four environments: an open lab bench, two growth chambers set at 25 °C and 28 °C (each with >90% relative humidity), and a screenhouse with fluctuating environmental conditions. ACP adults were exposed to contaminated leaf surfaces in sleeve cages for field trials. Half of the cages were misted three times daily. ACP was collected for assessment on days 1, 5, 10, and 15 post-exposure. In the lab, direct contact exposure showed 99% mortality within two weeks, with peak efficacy at 28 °C and high humidity. In the field, average mortality was 47%, increasing with exposure duration. Mycosis was observed in 30% of cadavers from misted cages and 15% from non-misted ones. These results underscore the potential of H. citriformis for ACP suppression, supporting its integration into citrus IPM programs under suitable environmental conditions.
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