One of our rose bushes is absolutely covered in aphids right now. Oddly enough, the ones next to it aren't.
To eat, aphids pierce the vessels in a plant where sap is transmitted; in doing this they can transmit viruses. While listening to 'This Week In Virology' last week I listened to an interesting story that has to do with aphids. Researchers from Penn State have been able to show that the cucumber mosaic virus can effectively lure aphids to infected plants by altering how the plants smell to make them more attractive to the aphids. When the aphids taste the plant, however, they quickly discover the ruse and leave for healthier plants... carrying the disease with them.
If you look closely at the picture, you can see 'honeydew.' This is the sticky substance that aphids secrete.
All of the new growth on this particular rose bush is covered in colonies of aphids. Tomorrow I'll try spraying them with a soap and water solution.