A controlled environment study of the effect of leaf physiological age on the movement of apterous Myzus persicae on sugar-beet plants

Apterous Myzus persicae were found to move frequently from leaf to leaf on sugar-beet plants in controlled environment conditions. It is suggested that aphid movement can be related to changes in the rate and content of translocate flow during leaf development. These changes make newly-emerged leaves nutritionally favourable to colonising aphids and make expanding leaves slowly wane in favourability during the process of ‘sink to source’ conversion leading to aphid dispersal from the leaf. Variation in temperature was not found to alter the rate of aphid movement or the period (measured in thermal time) that aphids spent on particular leaves. However, the lower temperature was found to increase the rate of aphid development, aphid size and fecundity; these effects could also be due to nutritional factors. This dispersal behaviour may be a tactic to maximise food intake by a polyphagous aphid and increase the probability that nymphs are deposited on nutritionally-favourable leaves. The implications of the interleaf dispersal of apterous M. persicae for within- and between-plant spread of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) are discussed.