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

The water lily aphid Rhopalosiphum nymphaeae (L.) (Homoptera:Aphididae ) is one of the potential pests of the genus Azolla Lam., an agronomic ally important aquatic fern used as green manure and as fodder. In thi s paper its life and fertility table was established by observing 70 v irginoparous females individually from birth to death on Azolla microp hylla Kaulf. under constant abiotic conditions. A rather short average development time of 6.1 days was observed. The maximum length of surv ival recorded was 24 days, and a linear relationship was found between age and survival. The fecundity averaged 36.8 larvae/female, but this appeared to be an age-specific parameter. Life table computation show ed a high intrinsic rate of increase (0.315 days(-1)), meaning that th eoretical populations could double every 2.2 days.