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:
- directly by sucking the host of part of its food supply and
water, producing necrotic spots in host tissue, and
- 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
Use of a hand lens will help in detection and identification, as
these organisms are quite small.