Field persistence and pathogenicity of Cordyceps fumosorosea for management of Diaphorina citri

The commercial fungal biopesticide product PFR-97 20% WDG, based on the entomopathogenic fungus Cordyceps fumosorosea (Cfr), is registered in the U.S.A. for foliar sprays on citrus. The persistence of Cfr suspensions (107 blastospores/mL) applied to grapefruit plants was evaluated under summer field conditions in southern Florida. Concurrently leaf disk bioassays were conducted to evaluate the pathogenicity of fungal residues on field-aged leaves against the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. The results demonstrated that Cfr persisted for at least 35 days under our field conditions and caused up to 40% ACP mortality when used in bioassays. There was a general trend of higher colony forming unit counts and a correspondingly higher ACP mortality with the residue age of field-treated leaves. We hypothesise that under certain environmental conditions the Cfr propagule residues will germinate, produce hyphae, phialides and develop conidia on the leaf phylloplane over time. During this study, an adult citrus leafminer Phyllocnistis citrella (Stainton), another important pest of citrus was observed mycosed with Cfr hyphae and subsequently attached to the citrus leaf. Our study shows that Cfr can potentially provide supplemental longer-term management for ACP. Abiotic and biotic factors that may affect the field activity of Cfr and other mycoinsecticides over time are discussed.