Insect Signs of Damage (3)

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Seed and Cone Damage

Seeds and cones can be affected in several ways by boring insects like weevils (cone or seed boring) or by insects feeding on the surface of a cone (cone scoring). Other insects with piercing- sucking mouthparts like Hemiptera, and rarely by insects with chewing mouthparts like Diptera larvae, can cause the cone to shrivel (shrivelled cones).


Shoot, Twig, Trunk and Root Damage

External bark damage is caused by mainly boring weevils, feeding on the bark of the trunk or twigs, leaving small holes or otherwise irregular wounds (bark scoring). Females of cicadas, tree hoppers or saw flies slit the bark and some jewel beetles and longicorn beetles chew small pits into the bark for oviposition (oviposition damage). Insects with piercing-sucking mouthparts can cause damage similar to the stippling damage of a leaf, causing a twig or shoot to wilt (feeding puncture). Oviposition and feeding by particular insects can cause galls on the stem and shoot.
Internal bark feeding usually affects the phloem and is caused for instance by larvae of bark beetles and pin- and shot-hole borers, that tunnel under the bark (phloem boring, under-bark boring and bark beetle damage).
Wood boring can affect the wood and/or the phloem of the trunk, branches or shoots (terminal boring and shoot boring,). Many Scolytidae and Platypodidae beetles are wood borers. The smaller larvae affect the softer tissues such as the phloem, but the bigger the larvae grow, the deeper they might tunnel into the wood. Ambrosia beetle damage is caused by the adults of these two families, boring small pin-holes or larger shot-holes through the bark right into the wood of living or dying trees and freshly cut lumber. Characteristic of this sort of damage is that there are no galleries under the bark and that the bore holes are kept free from saw dust. Furthermore, the holes are often stained by fungi like blue stain or affected by heart rot. Powderpost beetle damage is conspicuous due to the very fine, powder-like saw dust pushed out of the galleries made in trees and timber products. Termites (Isoptera) as well as some beetles like larval longicorn beetles (Cerambycidae) and weevils (Curculionidae) make irregular, interconnecting galleries in the heartwood and under the bark of living and dead trees and in timber products. Carpenter ants (Anthophoridae) are responsible for ‘honeycomb type wood boring. A ‘pipe’ is a big cavity excavated for the establishment of a termite nest.
Reactions of a plant to wounds indicate damage caused by insects. Sap and gum flow on the bark of a tree can be the result of insects like cicadas, pin- and shot-hole borers or bark beetles, damaging the bark, cambium or phloem. Sometimes a wound caused by insects results in the growth of a twig gall, an abnormal wood grain or crippled, malformed stems.

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Michael F. Schneider, 1999