Prevalence of Sitobion fragariae (Walker) over S. avenae (Fabricius) (Hemiptera: Aphididae) on wild cocksfoot grass (Dactylis glomerata) in south-east England

Individual cereal aphids of the species Sitobion avenae (Fabricius) and S. fragariae (Walker) were differentiated by their peptidase electrophoretic banding patterns; S. avenae has three diagnostic isoenzyme bands (PEP-3 to -5), whereas S. fragariae has one (PEP-1). Over 90% of 5389 individuals of these two species, collected from the grass Dactylis glomerata within 50 km of Rothamsted over the course of several years, were S. fragariae. The importance of D. glomerata and other non-cereal Gramineae species as alternative summer and overwintering hosts for S. avenae is discussed in relation to this finding.

Barley yellow dwarf viruses in, and aphids on, grasses (including cereals) in Tasmania

Samples of 2077 grasses and cereal plants representative of the Poaceae found in Tasmania were collected from a wide range of habitats throughout the State. Each sample was examined for infestation with aphids and then checked for infection with viruses causing barley yellow dwarf by both aphid transmission and serological tests. Aphid species found among the samples were Hyalopterus pruni, Rhopalosiphum maidis, R. padi and Sitobion fragariae. R. padi transmitted a vector non-specific type of barley yellow dwarf (PAV) and a vector specific type (RPV), either alone or together, while S. fragariae transmitted PAV alone and occasionally RPV when present in plants together with PAV. The other aphid species did not transmit. A total of 189 samples contained virus. Incidence was greatest in samples from the Bambusoideae subfamily (31%) and least in the Arundinoideae (4%). There was no difference in the level of infection between the native and introduced species that were represented. The Arundinoideae and Panicoideae were predominantly infected with RPV types, while the Pooideae, with the exception of Dactylis glomerata and Poa pratensis, were predominantly infected with PAV types. Many more infected plants contained both PAV and RPV (11.9%) than would have been expected had the two types of virus infected independently (2.5%). No infected plants were found among samples from 25 of the 56 species tested, and some of these may prove useful in breeding for resistance to barley yellow dwarf viruses.