Effects of Flowering Companion Plants on Black Bean Aphid (Aphis fabae Scop.) Abundance and Predatory Syrphid (Diptera, Syrphidae) Occurrence in Red Beetroot

This study aimed to determine the effect of phacelia (Phacelia tanacetifolia), dill (Anethum graveolens), and mustard (Sinapis alba) used as companion plants in red beetroot cultivation on the occurrence of Aphis fabae and predatory Syrphidae. Flowering plants were established along the edges of the beetroot crop. Aphid populations on beetroot were monitored, while syrphid larvae and pupae were collected from aphid colonies, and adult syrphids were sampled from flowers of the companion plants. The results show that beetroots grown without flowering companions had significantly higher aphid populations. The strongest aphid reduction occurred in red beetroot grown near phacelia, with aphid numbers 7.9–52.7 times lower than in control plots. Flowering strips increased the abundance of hoverfly larvae and pupae in aphid colonies, with the highest numbers recorded near dill. In total, 440 predatory syrphid larvae and pupae representing 11 species were collected from black bean aphid colonies on beetroots, whereas 3246 hoverfly adults from 46 species were observed on flowering plants, confirming their role in biological aphid control. In both cases, the eudominant group included E. balteatus, S. menthastri, and S. scripta. Dill flowers were the most attractive in terms of the number of captured syrphid specimens, whereas mustard showed the highest species diversity.