The use of pollen cues in resource location by a pollinator and a pest
This thesis presents evidence that pollen colour and odour may be used as cues in resource-location by pollen feeding insects; namely, the pollen beetle, Meligethes aeneus, a pest of cruciferous crops such as oilseed rape, Brassica napus (OSR), and the honey bee, Apis mellifera, an economically important generalist pollinator. Pollen beetle adults were attracted to both the colour and odour of OSR flowers in a wind tunnel, and linear track olfactometer studies showed that part of the attractive floral odour emanated from pollen. Beetles were attracted to OSR floral odour throughout their life cycle, indicating that 'innate' search images may be important in location of hosts upon which they can reproduce. Responses to floral odours from plants upon which the beetles do not reproduce varied according to the beetle's sex, life cycle phase and feeding history. There was some evidence for the use of pollen cues in oviposition, when oviposition incidence in male-fertile buds containing pollen and male-sterile buds without pollen were compared in the field. In feeding studies conducted in the laboratory, larvae displayed obligatory requirements for the resources from OSR flowers; they were unable to develop in field bean, Vida faba (FB) flowers. Although pollen consumption was not obligatory for larval survival and development, it reduced developmental time, and improved survival and 'fitness'. Restrained honey bees were able to learn the odours of OSR and FB pollens associatively, and could discriminate between them in the conditioned proboscis extension bioassay. This ability was confirmed in more natural conditions; free-flying bees discriminated between OSR and FB pollens on the basis of their odour, but showed a colour preference for the yellow OSR pollen over the grey pollen of FB. The relative importance of pollen as an attractive signal in OSR and FB is discussed.