PREDICTING SPRING MIGRATION OF THE DAMSON-HOP APHID PHORODON HUMULI (HOMOPTERA, APHIDIDAE) FROM HISTORICAL RECORDS OF HOST-PLANT FLOWERING PHENOLOGY AND WEATHER

1. Historical data of the spring migration of the damson hop aphid Pho rodon humuli recorded at Wye, Kent, and Rosemaund, Herefordshire, and the phenology of overwintering host-plant flowering, recorded at East Malling, Kent, were examined for possible associations. 2. Relationshi ps between mean temperature over a phenophase interval, defined by flo wering phenology of two overwintering host plum species (Myrobalan Pru nus cerasifera and Victoria Prunus domestica), which are overwintering hosts for P. humuli, and the start of migration of the aphid, versus the reciprocal of the interval duration (days), were significant for W ye (situated 32 km from East Malling) and at Rosemaund, a more north-w esterly site 260 km from East Malling. 3. Predictive sample reuse (PSR ) methodology was used to validate the potential of derived models to predict the start of migration of P. humuli at the two sites. Data for model determination and validation consisted of observations of P. hu muli migration over 20 years (1967-86) at Wye and 15 years (1972-86) a t Rosemaund. 4. The predictive performance of the host-plant flowering -aphid migration phenology models was compared with that of two other methods that use historical field data to predict insect life cycle ev ents. The host-plant flowering-aphid migration phenology model using t he beginning of flowering of Victoria gave the best prediction of the start of migration at Wye using one PSR criterion. The empirical degre e-day (DD) program gave the best prediction using an alternative crite rion. For the more distant Rosemaund site, the empirical DD program pe rformed best. 5. The potential use of host-plant phenology to predict 50% migration of P, humuli at Wye and Rosemaund was also investigated, and compared with the empirical DD programme using the PSR method. Th e host-plant phenology model gave good prediction of migration at Wye but poor prediction at Rosemaund, whereas the empirical DD programme g ave poor prediction at Wye and only reasonable prediction at Rosemaund . 6. The value of using historical data of host-plant and insect pheno logy to develop predictive models is illustrated, and the desirability of comparing the performance of alternative phenology models that may be used for prescriptive use is discussed.