Pathogenicity of Iranian isolates of Akanthomyces lecanii and A. muscarius on the black bean aphid (Aphis fabae Scopoli)

The Black bean aphid (BBA), Aphis fabae Scopoli (Hemiptera: Aphididae), is an important pest of agricultural and ornamental plants. Entomopathogenic fungi are important factors in the microbiological control of pests that are considered a good alternative for chemical insecticides. Isolation of novel potential IPF and evaluation of their efficacy against pests are primary steps for achieving a successful microbiological control program. In this study, the efficacies of three Iranian isolates of Akanthomyces lecanii (PAL6, PAL7, and PAL8) and an Iranian isolate of A. muscarius (GAM5) which had been isolated from two hemipteran pests, Pulvinaria aurantii Cock. and Aphis gossypii Glover, respectively, in citrus orchards of west Mazandaran (North of Iran), were evaluated against BBA.

Mortalities of the BBA nymphs and adults caused by different conidial concentrations (104, 105, 106, 107 108 conidia/ mL) of each fungal isolate during other days after treatment (DAT), 1–7 DAT, were determined under laboratory conditions.

All isolates were pathogenic to the aphid causing about 25% mortality. The efficiency of the isolates was not significantly different among the aphid life stages. When the isolate concentrations (up to 55%) and DAT (up to 53.13 times) increased, their effects increased significantly. The highest and lowest mortality rates were observed at concentrations 108 (12.83%) and 104 (5.86%) conidia/ mL, respectively. The highest effectiveness was recorded in seven DAT for all isolates, 15.14% mortality. At one DAT, the isolates caused about 1% mortality in the aphid population with the lowest effectiveness. The highest mortalities were observed for GAM and PAL7 isolates at six DAT, i.e., 16.83 and 16.67%, respectively. Furthermore, the lowest effectiveness was recorded for the isolates GAM and PAL7, at one DAT (<0.1% mortality), respectively.

The isolates had some potentials for microbiological control of the BBA. Time and conidial concentrations, are the critical factors determining the efficacies of the entomopathogenic fungi. The highest effectiveness can be achieved before six DATs. When the conidial concentrations increased, the obtained mortality by the isolates was enhanced. Due to the relatively low efficacies of the EPF and a lag time for getting sufficient mortality, integrated applications of the entomopathogenic fungi with other compatible control agents with faster effects such as biorational insecticides are recommended. However, the laboratory results should be supported with field or semi-field studies before recommending applications of the entomopathogenic fungi against the BBA aphids in greenhouse or field crops.