How Bees Respond Differently to Field Margins of Shrubby and Herbaceous Plants in Intensive Agricultural Crops of the Mediterranean Area

Abstract

(1) Intensive agriculture has a high impact on pollinating insects, and conservation strategies targeting agricultural landscapes may greatly contribute to their maintenance. The aim of this work was to quantify the effect that the vegetation of crop margins, with either herbaceous or shrubby plants, had on the abundance and diversity of bees in comparison to non-restored margins. (2) The work was carried out in an area of intensive agriculture in southern Spain. Bees were monitored visually and using pan traps, and floral resources were quantified in crop margins for two years. (3) An increase in the abundance and diversity of wild bees in restored margins was registered, compared to non-restored margins. Significant differences in the structure of bee communities were found between shrubby and herbaceous margins. Apis mellifera and mining bees were found to be more polylectic than wild Apidae and Megachilidae. The abundance of A. mellifera and mining bees was correlated to the total floral resources, in particular, to those offered by the Boraginaceae and Brassicaceae; wild Apidae and Megachilidae were associated with the Lamiaceae. (4) This work emphasises the importance of floral diversity and shrubby plants for the maintenance of rich bee communities in Mediterranean agricultural landscapes.

Keywords: agroecosystems; bees; biodiversity; conservation; floral edges; pollinating insects.

Figure 1

Numbers of genera (upper chart) per margin type on each sampling date and species (central) and the Shannon-Wiener index (lower) in pan traps in shrubby, herbaceous and control margins (means±SE). The numbers in the abscise (x) axe indicate the week of the year.

Figure 2

Trends in the numbers of wild bees (means ± SE), A. mellifera, wild Apidae, Halictidae, Andrenidae and Megachilidae captured in pan traps in shrubby, herbaceous and control margins. The numbers in the abscise (x) axe indicate the week of the year.

Figure 3

Visual sampling. Numbers of A. mellifera, wild Apidae, mining bees and Megachilidae observed in 2 × 2 m squares over a four-minute period in shrubby, herbaceous and control margins (means±SE). The numbers in the abscise (x) axe indicate the week of the year.

Figure 4

Trends in the floral resources (i.e., the proportion of cover*proportion of the plant in bloom) of different plant families in shrubby (upper) and herbaceous (lower) margins (means±SE). The numbers in the abscise (x) axe indicate the week of the year.

Figure 5

Annual averages of the different bee groups (A. mellifera, wild Apidae, mining bees and Megachilidae) observed in 2 × 2 m squares over a four-minute period in shrubby, herbaceous and control margins (means ± SE).

Figure 6

Plot of the scores of the first two components for the different plant families (symbols) and bee groups (red labels) in the of non-metric multidimensional scaling (NMDS). The black labels indicate the centroids for the different plant families.