One of the major aims of pollination ecology has been to understand the role and relative importance of different pollinator
species in both natural and agricultural systems. This study explores how the quantity of pollen delivered in a single visit to a
stigma (SVD) differs across insect species from a wide range of taxa (Orders: Hymenoptera, Diptera and Coleoptera) and assesses
the morphological and behavioral traits that lead to differences in pollen delivery. We used oilseed rape (OSR) (Brassica napus
L.), an economically important crop with open self-fertile flowers, as a test system. Behavioral traits and SVD were measured
in the field for individuals of all frequent flower-visiting species of OSR. Individuals were collected and morphological traits
were measured in the laboratory. The quantities of free pollen on different body parts of flower visitors, or ‘pollen load’, were
also measured. Behavioral and morphological traits were then assessed as predictors of SVD. The individuals that delivered
most pollen were (in order of greatest median number of pollen grains delivered): bumblebees (Bombus spp.), mining bees
(Andrenidae) and honeybees (Apis mellifera). However, all but one family of flies tested delivered a significantly greater median
number of pollen grains than the control, and most delivered more than sweat bees (Halictidae). Behavioral and morphological
traits were important in determining pollen delivery, with greater body length, hairiness and visit duration all resulting in greater
SVD. Pollen load was measured for a proportion of individuals and we found that for momentary flower visits, a greater quantity
of pollen on the head of the flower visitor was linked to a greater SVD. This study demonstrates that, while bees are important
pollinators in this system, many fly taxa are also effective at delivering pollen and this is linked to morphological and behavioral
traits found in both groups.
