SPECTRAL SENSITIVITY AND VISUAL CONDITIONING IN THE PARASITOID WASP TRYBLIOGRAPHA-RAPAE (HYMENOPTERA, CYNIPIDAE)

Spectral sensitivity of the wasp Trybliographa rapae (Westwood), a par asitoid of cabbage root fly larvae, was measured by the electroretinog ram (ERG) technique and by a complimentary behavioural technique, to 1 5 selected wavelength bands from 340 to 670 nm. Peaks of electroretino gram sensitivity were found in the ultraviolet, blue and green-yellow regions of the spectrum. This corresponds to known classes of photorec eptor present in the Hymenoptera. Behavioural peaks of phototactic att raction were found in the ultraviolet and green-yellow regions, but no t in the blue. No differences were observed between the sexes. We sugg est that ultraviolet and green-yellow wavelengths initiated 'escape' a nd 'foliage' orientated behaviour respectively. Blue wavelengths appea r to have a less specific function but may be important for colour dis crimination. Blue wavelengths did, however, become significantly more attractive to female wasps after a pre-experimental conditioning perio d involving exposure to blue wavelengths in combination with swede inf ested with cabbage root fly larvae. Thus T. rapae has been demonstrate d to show plasticity in its visually motivated behaviour. This may pro ve advantageous in the development of an artificial egg collecting tec hnique for this species.