Pathogenicity characteristics of the entomopathogenic fungus Cordyceps javanica IJ-tg19 to Acyrthosiphon pisum

Cordyceps javanica (Frieder. & Bally) (Hypocreales: Cordycipitaceae) is an important entomopathogenic fungus that is used as a mycoinsecticide to control pests such as aphids and whiteflies. However, few studies have been done on the pathogenicity of C. javanica to aphids. Using a virulence assay, we studied the entomopathogenic fungus C. javanica IJ-tg19, which has high virulence to the aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae). We compared conidial germination and activity of cuticle-degrading enzyme (subtilisin-like serine protease (Pr1) and chitinase) of C. javanica IJ-tg19 with the entomopathogenic strains Cordyceps fumosorosea (Wize) (Hypocreales: Cordycipitaceae) IF-1106 and Beauveria bassiana (Balsamo) (Hypocreales: Cordycipitaceae) BB-1339. The infection process of C. javanica IJ-tg19 strain to A. pisum was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that germination time of conidia of C. javanica IJ-tg19 and C. fumosorosea IF-1106 was shorter than that of B. bassiana BB-1339, and the germination rate was significantly higher than the BB-1339 strain. The germ tube of IJ-tg19 was accompanied by mucilage secretion during the body surface germination of A. pisum . The activity of total Pr1 and chitinase of IJ-tg19 reached their highest values at 48 h post-inoculation (PI), and the activities were significantly higher than those of IF-1106 and BB-1339. SEM and TEM observations showed that the infection peak was at 24 h PI, and mycelia had entered the hemocoel cavity of A. pisum at 48 h. These results indicate that C. javanica IJ-tg19 has several desirable attributes to act as an effective agent for the biological control of aphids.