Entomopathogenic fungus emits volatiles that attract its host, the Asian citrus psyllid, to infected conspecific cadavers

Behavioral responses of the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae) to the entomopathogenic fungus Cordyceps javanica were recorded using olfactometric assays, followed by volatile collection and analysis of the samples via gas chromatography – mass spectrometry (GC-MS). Y-tube olfactometer trials were conducted to evaluate the response of D. citri to conspecific cadavers mycosed with C. javanica. Psyllids used as odor sources in the treatment and control were incubated in separate vials containing one large citrus leaf for at least one week at 24°C with 100% relative humidity; the difference being the presence of fungal elements in the treatment and their absence in the control group. Specimens used as odor source were frozen following incubation to ensure psyllids' death prior to running all tests. During each olfactometric run, a single female psyllid was given five minutes to choose in a Y-tube between one side with the treatment odor and the other with the control odor. Data revealed the attraction of healthy D. citri to conspecifics infected by the insect-killing fungus C. javanica. Based on these findings, volatiles emitted by contaminated psyllids were collected through solid phase microextraction and compared with that of non-contaminated ones. Several compounds have been identified in GC-MS analyses that may explain the preference of D. citri for infested conspecifics.