Abstract
Pandora neoaphidis and Entomophthora planchoniana (phylum Entomophthoromycota) are important fungal pathogens on cereal aphids, Sitobion avenae and Rhopalosiphum padi. Here, we evaluated and compared for the first time the virulence of these two fungi, both produced in S. avenae cadavers, against the two aphid species subjected to the same exposure. Two laboratory bioassays were carried out using a method imitating entomophthoralean transmission in the field. Healthy colonies of the two aphid species were exposed to the same conidial shower of P. neoaphidis or E. planchoniana, in both cases from a cadaver of S. avenae. The experiments were performed under LD 18:6 h at 21 °C and a successful transmission was monitored for a period of nine days after initial exposure. Susceptibility of both S. avenae and R. padi to fungal infection showed a sigmoid trend. The fitted nonlinear model showed that the conspecific host, S. avenae, was more susceptible to E. planchoniana infection than the heterospecific host R. padi, was. In the case of P. neoaphidis, LT50 for S. avenae was 5.0 days compared to 5.9 days for R. padi. For E. planchoniana, the LT50 for S. avenae was 4.9 days, while the measured infection level in R. padi was always below 50 percent. Our results suggest that transmission from conspecific aphid host to heterospecific aphid host can occur in the field, but with expected highest transmission success to the conspecific host.
Highlights
Sitobion avenae (Fabricius, 1775) and Rhopalosiphum padi (Linnaeus, 1758) aphids are serious pests, commonly coexisting in cereal fields [1,2,3]
It is not known to which extent infection can be transmitted between S. avenae and R. padi in the field and if an epizootic in one of these aphid species can result in infection in the other aphid species
To understand the transmission of a fungal pathogen between aphid host species occurring in the same crop, we need comparative virulence bioassay studies mimicking the situation occurring in the field
Summary
Sitobion avenae (Fabricius, 1775) and Rhopalosiphum padi (Linnaeus, 1758) aphids are serious pests, commonly coexisting in cereal fields [1,2,3]. Both species can cause economic damage through their feeding activity and their role in the dissemination of phytoviruses, such as the Barley Yellow Dwarf. Virulence studies with hypocrealean insect pathogenic fungi, such as species from the genera Beauveria and Metarhizium, can be done by subjecting the target insect to suspensions with a predefined, known concentration of conidia. This is possible because these hypocrealean fungi have small, dry conidia which can readily be dissolved in water supplemented with a detergent [12,13]
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