ANTIBIOSIS AND ANTIXENOSIS OF CHRYSANTHEMUM CULTIVARS TO THE APHID APHIS-GOSSYPII

An assessment was made of the antibiotic and antixenotic resistance of three cultivars of autumn flowering chrysanthemum (derived from Dendr anthema morifolium (Ramat) Tzvelev and D. indicum(l.) Desmoulins) to t he aphid Aphis gossypii Glover. Antibiosis was also assessed at the to p, middle and lower leaves of the plant. The three cultivars showed a range of resistance with Hero being the most susceptible, Surfine the most resistant and Purple Anne intermediate. There was a trend for ant ibiosis to improve with position down the plant, however there were cu ltivar by position interactions. Antixenosis was assessed at two level s, the first being under conditions where the aphid had complete acces s to the plant in caged choice assays and the second being under condi tions where the aphid only had host odour to assess under olfactometer choice conditions. Preferences under the caged choice conditions foun d Hero to be the most preferred cultivar while there was no preference shown between Purple Anne and Surfine. However, olfactometer assessme nts showed Hero to be the least preferred of the three cultivars and, again, no preferences could be found between Purple Anne and Surfine.