The transfer of pollen from oilseed rape to a weedy relative (wild radish) by insects was studied with the aim of predicting the risk of the release of a transgene (resistance to herbicide conferred to oilseed rape) in the environment. The pollinating entomofauna present on both plant species was compared in a preliminary study. Two trials were conducted. At site A, the trial consisted of an area of oilseed rape (780m²), including 1m² of wild radish in the centre. At site B, there was a 750m² area of wild radish, including some plants of oilseed rape. The insect diversity, abundance and foraging behaviour (number of flowers visited /min) were observed on both sites simultaneously. Moreover, at site A, the movement of insects between both plant species were observed in the central place by several methods (individual observation, passing ratio of a foraging population during 3 minutes, flower constancy and avoidance of wild radish). In addition, some parameters of floral attractiveness were assessed (flower density, morphology, pollen and nectar production) to understand insect preference for one of the plant species. The results showed both plants had the same flower density at full flowering but differed in their floral morphology and did not offer equal quantities of food (wild radish had deeper and narrower corolla, smaller petals, less pollen and more variable amounts of nectar). Both plants were attractive to pollinators but to differing degrees, depending on the insect taxon. Wild radish was significantly less visited by honeybees. With regard to the risk of pollen transfer between the two species, results showed that when honeybees were foraging on an area predominantly planted with oilseed rape (site A), they avoided wild radish because of their high flower constancy. The constancy of bumblebees differed between species: Bombus terrestris were more constant to oilseed rape, whereas Bombus lapidarius were more constant to wild radish. This led to a relatively low frequency of movement between plant species although bumblebees visited flowers at a higher rate than any other pollinators. Solitary bees and flies seemed to be indifferent to the plant species. The role of each insect group in pollen transfer between oilseed rape and wild radish is discussed with regard to its relative density and foraging behaviour.