Resumen
The objective of this study was first to determine whether the chemical defence of lupin is more effective against the generalist aphids that occur on lupins than the host specific, M. albifrons. Secondly, to determine whether the host specific aphid shows an increase in performance over time if it is reared on sweet lupin and whether the process is reversed when transferred back to a bitter variety of lupin. Of the lupin cultivars tested only those with strongly reduced alkaloid contents were acceptable as host plants by the generalist species of aphid tested, and only M. albifrons reproduced on the ?bitter? cultivars. In order to define the performance of M. albifrons, developmental time, mean relative growth rate and number of embryos were recorded for two strains reared for several generations on a bitter cv. of lupin and then transferred for several generations to sweet lupin and then reared again on a bitter cv. of lupin. The performance of M. albifrons was not better on lupins rich in alkaloids. However, the results also indicate that this aphid can adapt and thrive on a previously resistant cultivar within five generations even when reproducing parthenogenetically and that this change is reversible.