Effect of Flower Strips on Aphid Antagonists in Sugar Beet Fields

Autumn-sown annual or perennial flower strips support antagonists of aphids, which are vectors of virus yellows, a severe disease in sugar beet. The effectiveness of these strips is influenced by floral composition, sowing time point and surrounding landscape elements.

Biological control aims to reduce pesticide use by increasing populations of natural enemies that target pest species. The effectiveness of flower strips (FS) for this purpose has been demonstrated in different crops. However, in spite of the significant challenge posed by the green peach aphid (Myzus persicae) and the black bean aphid (Aphis fabae), which introduce virus yellows into the fields early in the season, research on the role of FS in sugar-beet crops remains limited.

Agroscope therefore conducted a study to identify the most suitable FS type for supporting biological control in sugar beet. To this end, we quantified flower availability and composition of different FS types in early spring, recorded the abundance and composition of aphid antagonists across different FS types, and analysed the influence of surrounding landscape elements on their presence.

To do this, three FS types were each sown on ten sugar beet fields managed without insecticide. These were compared to sugar beet strips managed with or without insecticide, the latter two treatments serving as controls.

Overwintering flower strips are beneficial for aphid antagonists

Many adult aphid antagonists are dependent on the presence of flowers to maintain their populations. Particularly in the sugar-beet system, early-season flower availability is critical for ensuring that aphid antagonists are present early enough to control pests in a timely manner. Such flowers were abundant in the autumn-sown annual and perennial FS but absent in spring-sown annual FS. Moreover, aphid antagonists were more abundant in the first mentioned FS types than in the spring-sown annual FS and in the controls, demonstrating the link between flower availability and the presence of aphid antagonists.

Different hoverfly communities

Overall, aphid antagonist composition did not differ significantly between the autumn-sown annual and the perennial FS. By contrast, hoverfly communities differed between these two FS, most likely owing to the different composition of the flowering plant species.

Mixed response of aphid antagonists to landscape elements

Forest and flowering elements had no effect on the overall abundance of aphid antagonists. By contrast, a closer look at specific predator groups revealed a positive association between Braconidae and forest cover within a 500m radius, while hoverflies showed a negative association with forest cover at the 2000m scale..