Introducing Erynia neoaphidis into a field population of Aphis fabae: form of the inoculum and effect of irrigation

SUMMARY The effect of treating field populations of Aphis fabae on spring‐sown field beans with different preparations of the entomogenous fungus Erynia neoaphidis, with and without irrigation of the crop, was examined at Rothamsted in 1979. The fungus applied on 21 June as the triturated cadavers of fungus‐killed aphids established infection in the host population as effectively as by distributing living laboratory‐infected aphids. Although the introduced fungus, together with other species present naturally, killed more than 70% of aphids in late July, it failed to multiply fast enough to protect the crop adequately. An application of an homogenate of the fungus grown on agar plates failed to establish infection. From 25 June to 28 July there was little rain and irrigation greatly increased the proportion of aphids killed by E. neoaphidis during late July confirming that the spread of this fungus can be limited by dry conditions.