Changes in the Growth-regulator Content of Plum Infested with Fruit Tree Red Spider Mite, Panonychus ulmi (Koch)

Extracts and diffusates were collected from the extending regionof Brompton plum shoots shortly after a reduced rate of extensionwas detected in those infested with fruit tree red spider mites.Bioassays showed greater amounts of gibberellin-like substancesand smaller amounts of auxin-like substances, with the exceptionof IAA, in the mite-infested material. Although the extendinginternodes of infested plants contained significantly less IAAthan the controls, there were similar amounts of IAA in theexpanding leaves of infested and control plants.