SELECTION OF AZOLLA FORMS RESISTANT TO THE WATER LILY APHID, RHOPALOSIPHUM-NYMPHAEAE - SUSCEPTIBILITY OF AZOLLA FORMS TO RHOPALOSIPHUM-NYMPHAEAE

The least expensive method for controlling the water lily aphid, Rhopa losiphum nymphaeae (Homoptera: Aphididae), would be to select a more r esistant variety of Azolla. Therefore the susceptibility of 6 species of Azolla totalling 12 forms, was analysed by the use of aphid surviva l and cumulative fecundity. For each form, a minimum of 50 to 140 virg inoparous females were followed individually from birth to death. Six forms of three species appeared to be totally resistant, as a mortalit y rate of 100% was recorded after 4 days; thus insects were unable to reach adulthood. For one form, adults were obtained but died within 11 days and fecundity was poor. The other five forms were more susceptib le, and significant differences were found in the total number of offs pring after one generation. These results show differences in suscepti bility between different forms of Azolla, and thus strongly support th e possibility of cultivating more resistant varieties.