Food for insect pollinators on farmland: insect visits to flowers of annual seed mixtures

Intensification of agriculture in recent decades has impoverished farmland for insect pollinators by removing their food plants. Arable farmland can be enhanced as a habitat for these insects by growing annual nectar-and pollen-producing herbaceous plants for them in non-cropped areas such as set-aside and field margins. In 1996 and 1997, observations were made in Hertfordshire, UK, on the flowering phenology and flower-attractiveness to visiting Hymenoptera, Diptera and Lepidoptera of plots sown to mixtures of six annual flowering plant species: borage (Borago officinalis), buckwheat (Fagopyrum esculentum), cornflower (Centaurea cyanus), mallow (Malva sylvestris), marigold (Calendula officinalis) and phacelia (Phacelia tanacetifolia) in different proportions. The mixtures had good agronomic and biological properties. They established and flowered well from a range of seed rates and sowing-dates. They attracted a diversity of flower-visiting insects, including the honey bee and eight species of bumble bee amongst 16 species of aculeate Hymenoptera, 17 species of Diptera, mostly syrphids, and six species of Lepidoptera. Sequential sowings provided nectar and pollen from early summer to late autumn during the period after arable crops had finished flowering and food for pollinators was scarce. Different insect species were favoured by different sowing-dates and plant species.