Distribution of bird cherry-oat aphids (Rhopalosiphum padi (L.)) in relation to landscape and farming practices

Apterous aphids show varying degrees of aggregation in the field. Both alate and apterous Rhopalosiphum padi (L.) were compared in terms of degree of aggregation in relation to landscape features and farming management (conventional vs. organic). Alate R. padi were clearly aggregated, but no effect of landscape features or farming management was found on the degree of aggregation. Apterous R. padi were aggregated, and to a degree that varied according to field. Aggregation tended to be lower in landscapes with high perimeter-to-area ratios of the fields, but there was no significant difference between organically and conventionally managed fields. The fields with low aggregation had few alate, low R. padi population growth rate and therefore a low abundance.