Evaluation of Isaria fumosorosea (Hypocreales: Cordycipitaceae) for control of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

A laboratory bioassay was developed to evaluate strains of Isaria fumosorosea Wize, against Diaphorina citri. Up to 100% of adult psyllids were killed at concentrations between 10⁶ and 10⁷ blastospores/ml after 12 days, with derived LC₅₀ values (at 7 days post treatment) between 1.4 × 10⁵ and 2.0 × 10⁶ blastospores/ml for strains ARSEF 3581, FE 9901 and Apopka-97. A significantly higher value (1.5 × 10⁷) was obtained with a conidial formulation of Apopka-97. Average survival times were dosage dependent, i.e. between 10.2 days at 10³ blastospores/ml and 3.5 days at 10⁸ blastospores/ml. Rates of mycosis were also dosage dependent, with up to 100% sporulation on cadavers at 10⁸ blastospores/ml but declining at lower concentrations. The Apopka-97 strain (commercially available as PFR-97) was tested against established D. citri infestations in potted citrus in greenhouse cages. Treatments at label rates reduced psyllid populations by approximately 50% over 3 weeks. The combination of PFR-97 with emulsifiable oils (0.25% v/v) did not increase psyllid mortality compared with either agent alone. Imidacloprid applied as a drench killed 100% of psyllids within 3 weeks. Subsequent greenhouse tests during humid conditions were hampered by natural dissemination of I. fumosorosea to untreated psyllids, suggesting that this fungus is spread by air movement and may be highly effective under very humid conditions. In later tests, a Cladosporium sp. rapidly colonised psyllid cadavers and leaf surfaces, but was not pathogenic in laboratory tests. Our studies confirm the potential of I. fumosorosea to be used in IPM strategies for D. citri that rely on other tactics, such as insecticidal oils and native or introduced biological control agents.