Brassica seed crops are grown throughout New Zealand and worldwide, and inter-crop and crop-weed contamination through gene flow is a major concern. For Brassica, large arthropods (body length > 3 mm), particularly honey bees, are the most important pollinators and are considered key vectors of pollen. Small arthropods (body length < 3 mm) are also abundant in Brassica crops but their role as pollinators is rarely assessed. Numerous small arthropods (particularly Diptera and Thysanoptera) were recorded within cages surrounding pak choi inflorescences that excluded large arthropods. Inflorescences inside these cages set seed, but seed set was significantly reduced compared with inflorescences in cages that were hand-pollinated and uncaged inflorescences. Although the presence of large arthropods significantly increased seed sets, the role of small arthropods and wind cannot be excluded in pak choi pollination. Further studies are required to fully determine the role of small arthropods in long-distance pollen flow.
