Distribution of Eggs of the Black Bean Aphid, Aphis fabae Scop., on the Spindle Bush, Euonymus europaeus L., with Reference to Forecasting Infestations of the Aphid on Field Beans

SUMMARY Eggs of Aphis fabae were laid on the spindle bush, Euonymus europaeus, in the bud and twig axils, on leaf or twig scars and in cracks on the rough bark which formed after about three years. The numbers of eggs laid on individual first-year twigs on a particular bush increased with the numbers of buds that it bore, which were directly related to twig length. Very few eggs were laid on weak first-year twigs. On cut bushes in a hedgerow, the length of first-year twigs was inversely related to the age of the bush since cutting. Eggs laid in bud and twig axils on first-year twigs provided an effective measure of numbers on the whole bush for, although some were laid elsewhere, the proportion on first-year twigs was not significantly affected by the changes in the overall egg density except on very poorly growing bushes. The estimate of egg numbers was improved by excluding poorly growing bushes and by not sampling individual twigs shorter than 5 cm or those with only a single bud. Variability, particularly between sampled bushes of differing vigour, was also decreased if numbers were expressed as ‘eggs/bud’ instead of ‘eggs/twig’.