Entomophthoralean fungi overwinter with the bird cherry-oat aphid on bird cherry trees

In Scandinavia, the bird cherry-oat aphid Rhopalosiphum padi overwinter as eggs on the bird cherry tree Prunus padus. Branches of P. padus were collected at the late February / early March from 17 locations in Norway over a three-year period. We found 3599 overwintering aphid eggs, 59.5% of which were dead. Further, a total of 879 overwintering fungus-killed cadavers were observed. These cadavers were found close to bud axils, where overwintering eggs were also usually attached. Cadavers were infected with either Zoophthora cf. aphidis or Entomophthora planchoniana. All the fungal-killed cadavers were filled with overwintering structures of Z. cf. aphidis (as resting spores) or E. planchoniana (as modified hyphal bodies). We found a significant negative cor-relation between eggs and cadavers per branch. However, both numbers of eggs and cadavers varied greatly between years and among tree locations. This is the first report of E. planchoniana overwintering in R. padi ca-davers as modified hyphal bodies. We discuss whether P. padus may act as an inoculum reservoir for fungi infecting aphids in cereals in spring.

Automated summary

In Norway, the overwintering behavior of the bird cherry-oat aphid Rhopalosiphum padi on the bird cherry tree Prunus padus was studied over a three-year period. A total of 3599 overwintering aphid eggs were found, with 59.5% of them being dead. Additionally, 879 overwintering fungus-killed cadavers were observed, which were infected with Zoophthora cf. aphidis or Entomophthora planchoniana. The study suggests that Prunus padus may serve as a reservoir for fungi infecting aphids in cereals during spring.