Damage to Leaves Caused by Fruit Tree Red Spider Mite,Panonychus Ulmi (Koch)

Fruit tree red spider mites, Panonychus ulmi (Koch), were caged on the upper or lower surface of plum or apple leaves; the speckles resulting from their feeding were visible only from the surface on which they fed. Histological studies revealed that mites on the lower surface do not damage the uppermost layer of palisade mesophyll cells. Mites on both surfaces at first feed predominantly on tissues close to the veinlets, damaging mesophyll and bundle sheath cells. Bronzing, which develops later, is associated with damage to mesophyll cells further from the veinlets. Larger speckles are seen when mites have fed on leaves when they were still expanding, causing cells adjacent to those directly damaged to develop abnormally, and the leaves are distorted locally; in some cases a phellogen is formed.