The majority of sap-sucking insects are in the orders Hemiptera (true bugs) and Homoptera (aphids, leaf and plant hoppers, and scales). Most of these insects are relatively small in size and injure the host in two ways:

1. directly by sucking the host of part of its food supply and water, producing necrotic spots in host tissue, and
2. indirectly by introducing plant diseases.

The mouthparts of these insects and mites are formed into beak-like structures that are used to pierce host tissues and suck the sap. Damage by sap-sucking insects is often mistaken as a pathogen induced disease. A few of the sap-sucking insects are able to kill their hosts outright, but most reduce growth rates and weaken the tree. Trees injured by these insects may succumb to secondary insects or fungal diseases. Signs of sap-sucking insect injury consist of enlarged growths or galls, leaf curling, bleaching, or yellowing of foliage. Conifers are more severely injured than hardwoods.

In the Southwest, there are several sap-sucking insects that cause noticeable damage to trees and shrubs, but they have not affected forests at the landscape scale. Their impacts are typically more important to shade trees and ornamentals. However, a spruce aphid, Elatobium abietinum, has been severely impacting spruce forests and ornamentals in some areas of the Southwest since the 1990s.

Use of a hand lens will help in detection and identification, as these organisms are quite small.

References:  24, 41