ARS | Publication request: Observations on the entomopathogenic fungus Hirsutella citriformis attacking adult Diaphorina citri (Hemiptera: Psyllid) in a managed citrus grove

Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 5, 2012
Publication Date: March 28, 2012
Citation: Hall, D.G., Hentz, M.G., Meyer, J.M., Boucias, D.G. 2012. Observations on the entomopathogenic fungus Hirsutella citriformis attacking adult Diaphorina citri (Hemiptera: Psyllid) in a managed citrus grove. Biocontrol. 57:663-675.

Interpretive Summary: A field study was conducted to characterize the phenology of the entomopathogen Hirsutella citriformis infecting adults of the Asian citrus psyllid. On the average, 23 percent of adults observed on mature leaves were killed by this fungus. Infected cadavers of the psyllid were most abundant during the fall and winter months. Infected psyllid cadavers were nearly absent each spring, presumably because relative humidity levels were suboptimal for the fungus at this time. Infected cadavers, which serve as point sources for new infections of the fungus in psyllids, were observed to remain on leaves for a mean of 68 days (one cadaver remained on a leaf for 168 days). A laboratory investigation was conducted into the toxicity to the fungus of six chemicals commonly used for pest management in citrus. Citrus growers interested in capitalizing on the fungus as a biological control agent of the psyllid should avoid applying high rates of copper hydroxide, oil or sulfur.

Technical Abstract: A two-year field study was conducted in an orange grove (0.7 ha) in Florida to characterize the phenology of the entomopathogen Hirsutella citriformis Speare infecting adults of the Asian citrus psyllid, Diaphorina citri Kuwayama. On the average over the two-year study, 23 percent of adults observed on mature leaves were killed by H. citriformis. Mycosed cadavers were most abundant during the fall and winter months, with the maximal percentage of adults mycosed sometimes exceeding 75 percent. Mycosed cadavers were nearly absent each spring, presumably because relative humidity levels were suboptimal for the fungus at this time. Based on dispersion analyses, a monitoring plan for mycosed cadavers would best include multiple samples in individual trees as well as multiple tree samples throughout a grove. Mycosed cadavers, which serve as point sources for new infections of the fungus in psyllids, were observed to remain on leaves for a mean of 68 days (one cadaver remained on a leaf for 168 days). Rainfall was positively correlated with the number of days cadavers remained on leaves while mean daily air temperature was negatively correlated. Mycosed cadavers were abundant in the summer during 2006, but not during 2007. This may have been a density-dependent consequence of psyllid host populations being low in 2007. Alternatively, combination sprays of oil and copper applied during 2007 may have suppressed the fungus. This latter possibility prompted a laboratory investigation into the toxicity to H. citriformis of six chemicals commonly used for pest management in citrus. At maximum label rates, copper hydroxide, petroleum oil, and elemental sulfur each significantly reduced the infectivity of a laboratory culture of H. citriformis while copper sulfate pentahydrate, aluminum tris and alpha-keto/humic acids did not. This finding indicates that citrus growers interested in capitalizing on H. citriformis as a biological control agent of D. citri should avoid applying high rates of copper hydroxide, oil or sulfur.