ARE APHID MEAN RELATIVE GROWTH-RATE AND INTRINSIC RATE OF INCREASE LIKELY TO SHOW A CORRELATION IN PLANT-RESISTANCE STUDIES

In a study of the performance of Aphis fabae Scop. on 6 British and 3 Polish cultivars of Vicia faba L., the aphid showed a poor mean relative growth rate (MRGR) On the Polish cultivar Hangdown Bialy (p = < 0.05). Measurements of fecundity, the intrinsic rate of natural increase (r(m)) and MRGR were obtained on a large number of individual plants. Correlations between MRGR and both r(m) or fecundity for individual plants across cultivars were not significant. Although within cultivars, individual plants of Aquadulce and Relon showed significant positive correlations of aphid MRGR on fecundity and r(m) respectively, the two correlations accounted for less than 20% of the variation in MRGR and no such correlations were found for the other seven cultivars. Although MRGR showed the highest residual variance (in relation to the mean) of the three performance indicators assessed, it nonetheless proved to provide the best discrimination between the cultivars tested. It is suggested that this is because MRGR is less subject to `maternal influence' than fecundity or r(m).