Virulence of an Aphid-Derived Isolate of Beauveria bassiana (Fungi: Hyphomycetes) to the Hop Aphid, Phorodon humuli (Homoptera: Aphididae)

The potential for biological control of the hop aphid using an aphid-derived isolate of Beauveria bassiana was investigated in the laboratory and field. In initial bioassays using conidial suspensions at dosages ranging from 10 4 to 10 8 a conidia/ml, the isolate exhibited a high level of virulence to Phorodon humuli (Schrank), yielding a LC 50 of 1.37 × 10 5 conidia/ml. LT 50 values decreased with increasing conidial dose, being 11.1 ± 4.2, 8.4 ± 4.0, 5.0 ± 1.5, 3.6 ± 1.5, and 3.1 ± 1.1 d at 10 4 , 10 5 , 10 6 , 10 7 , and 10 8 conidia/ml, respectively. A potential for long-term control was demonstrated when conidial suspensions were applied to aphid-infested potted hop plants. Aphids increased only slightly during a 4-wk period on potted hop plants treated with a suspension of 107 conidia/ml. This was significantly lower than the net increase found on the controls and on plants treated with a suspension of 10 5 conidia/ml. However, there was no mycosis detected in aphids when a 107 conidia/ml suspension was applied in an aphid-infested commercial hop yard.