Swedish University of Agricultural Sciences Department of Entomology Box 7044, 750 07 Uppsala, Sweden.
The host alternating Bird Cherry-Oat aphid, Rhopalosiphum padi (L.), overwinters on Prunus padus L. and lives during the summer on a wide range of grasses. It is an important pest in Swedish cereal crops. Potential effects of mixing barley genotypes on aphid acceptance were studied. Four barley varieties were used in different combinations and, with a compressor supported system, air was lead from one plant and then over a second plant. The effects of this treatment on the second plants were evaluated with regards to changes in host plant acceptance by apterae of R. padi. Leaf temperatures were measured with an infra-red camera. In an untreated state, the four barley varieties did not show differences in attractivity to aphids or in leaf temperatures. After treatment, significant changes were found. Thus, our results indicate that possible changes in aphid plant acceptance may be induced when some varieties are exposed to air from other varieties. The four varieties were mixed in a field experiment and aphid settling tests were done in situ. Significant effect of the genotype combinations showed that the effect shown in the laboratory represents a mechanism which is also effective under field conditions.