Visual and Olfactory Cues for Catching Parasitic Wasps (Hymenoptera: Scoliidae)

Abstract

Scoliid wasps (Scolia spp.) are day-flying flower visitors. Earlier field observations indicated preference of Scolia hirta, S. flavifrons and S. sexmaculata for a combination of a light blue colour and a quaternary floral blend [(E)-anethol, 3-methyl eugenol, 1-phenylethanol and lavandulol] constituents of traps used for catching the scarabs Cetonia aurata aurata and Potosia cuprea. Subsequent field experiments for Scolia hirta, S. flavifrons and S. sexmaculata in Hungary, Croatia and Turkey, respectively, comparing different colours and floral blends previously found efficient for catching several scarab species, confirmed observations on the preference of scoliids for the Cetonia/Potosia trap. When investigating the relative importance of the colour and the quaternary floral blend released from the Cetonia/Potosia trap for S. hirta, joint application of the visual and chemical cues resulted in a significant increase of catches, compared to those in traps containing only one of the cues, or in unbaited traps with no colour. An explanation of the activity of the Cetonia/Potosia trap on scoliid wasps can be that, since the wasps feed on flowers and the bait of the Cetonia/Potosia trap comprises common floral compounds, it represents olfactory stimuli essential in host plant-finding. Role of the blue colour also seems to be important, however, more detailed comparative studies, including different colours and chemicals, are necessary to better understand interactions mediating host plant-finding. Possibilities of practical application of the Cetonia/Potosia trap for monitoring S. hirta and S. flavifrons are discussed.