Is it necessary to spray roses for aphids?  The published scientific article below suggests that it is not necessary.

Author: MILES P W
Author Address: WAITE AGRIC. RES. INST., UNIV. ADELAIDE, ADELAIDE, S. AUST.
Title: DYNAMIC ASPECTS OF THE CHEMICAL RELATION BETWEEN THE ROSE APHID MACROSIPHUM-ROSAE AND ROSE BUDS
Published in: Entomologia Experimentalis et Applicata, volumn 37, pages 129-136, (1985).
Abstract: "Dynamic aspects of the chemical relation between the rose aphid [Macrosiphum rosae] and rose buds.In warm weather, M. rosae (L.) walks off buds of hybrid tea roses during a critical period coinciding with the opening of the sepals. This behavior could not be related to histologically detectable barriers to feeding, nor to changes in the water content of the tissues or in their composition with respect to total soluble carbohydrate, amino nitrogen or phenolic compounds; major changes in tissue chemistry, effected by spraying the bushes with urea, did not affect the time at which the aphids left the buds. Tissue sap expressed from stems and sepals showed a significant increase in catechin content after, rather than during, the critical period. Once expressed, however, sap from buds at the critical stage showed a sharp in vitro rise in catechin content over a few hours, up to levels approximating those against which the insects discriminated in choice tests. The insects could well be sensitive to a developing capacity of tissue to accumulated catechin, possibly in response to their feeding activity."