Use of ryegrass strips to enhance biological control of aphids by ladybirds in wheat fields

Non-crop habitats may play a vital role in conservation biological control. This study tested the effect of ryegrass （Lolium multiflorum L.） strips on aphid and la- dybird populations in adjacent winter wheat fields. The field experiment was conducted in three ryegrass-margin wheat plots and three control plots in 2010 in North China. In spring, the same aphid species, Sitobion miscanthi （Takahashi）, was found in both the ryegrass strips and wheat plots. The population density of ladybirds in the ryegrass strips （3.5 4- 0.9/m2） was significantly higher than in the wheat plots （1.5 4- 0.5/m2）. We cut the ryegrass, forcing the ladybirds to migrate to the wheat fields. Three and eight days after cutting the ryegrass, the aphid numbers in the ryegrass-margin wheat plots decreased significantly： they were 19.9% and 53.6%, respectively, lower than in control plots. In the early period of ladybird population development, the percentage of larvae was greater in the ryegrass-margin wheat plots than in controls, and the peak number of pupae in the ryegrass-margin wheat plots occurred 5 days earlier than in the control plots. The results suggest that ryegrass strips may promote the development of ladybird populations. Cutting ryegrass can manipulate ladybirds to enhance biological aphid control in wheat fields. The efficiency of this management approach is discussed.