There are numerous species of bark beetles which attack weakened or dying pines, spruces and firs. The most common species belong to the genera Dendroctonus and Ips. Numerous species of these beetles are always present where conifers are grown.
All conifers may be attacked by various species of bark beetles. Usually, pines and spruces will only be attacked if they are under environmental, cultural or disease stress.
Bark beetle adults usually attack trees which are under stress, have been freshly killed or are in the process of dying. Occasionally adults will lay eggs in trees which were temporarily under stress and the larvae may girdle these live trees when the tunnels of several individuals cut off the plant vascular system. Bark beetles which kick out sawdust-like shavings when they enter the tree trunk are making use of a freshly killed tree, and are not the cause of death. Occasionally, bark beetles can attack apparently healthy trees in sufficient number to gain a foothold. This often happens where a large number of pines or spruces were damaged from storms or fire and the large population of new bark beetles have nothing else to attack.
These cylindrical, brown to black beetles are usually very small, 1/6 to 1/8-inch, but can cause considerable damage. Fortunately, most species in the northeastern United States only attack weak or dying trees. Some species attack branches or cones but the ones which can kill a tree attack the trunk.
The pine engraver, Ips pini (Say), will serve as an example scolytid- type bark beetle. Adults overwinter in pupal cells hollowed out of the bark. These adults emerge in the spring and females locate a suitable tree for egg laying. A female will chew a round hole into the bark and go down to the cambium layer. A male soon joins the female and mates with her in this "nuptial chamber." The female then deposits three to six eggs in galleries set off from the central chamber. The eggs hatch into small white grubs with brown heads. These grubs continue to tunnel away from the central chamber. Upon completing their growth, the grubs burrow into the bark and pupate. Up to three generations per season may occur in New York to Ohio.
Generally, bark beetles do not attack small or vigorously growing conifers. Attacks occur when trees have been damaged or are weakened by over crowding, drought, saturated soils or disease.
Strategy 1: Cultural Control - Sanitation - Remove any dead or dying trees and grind, chip or burn the remains. Wind blown or burned conifers nearby should be removed and destroyed.
Strategy 2: Cultural Control - Maintain Health of Trees - Conifers planted in good soil and properly fed and pruned will rarely be successfully attacked by bark beetles. During periods of drought, water the trees. In heavy soils, attempt to provide drainage.
Strategy 3: Insecticide Sprays for Recently Transplanted Trees - Larger pines and spruces (tree diameter of four inches or more) which have been recently transplanted may need protection for the first year, especially if drought conditions are encountered. Treat the trunk and major branches with a protectant insecticide in mid-May, early July and late August. See Bulletin 504 for a listing of insecticides registered for borer protection.
Strategy 4: Insecticide Protectant Sprays - Occasionally, several trees in a wind break or landscape planting will be attacked by bark beetles. This generally indicates that the trees were weakened by something and the surrounding trees may also be under stress. Remove the attacked trees and apply a protectant spray to the nearby trees until they are showing signs of good growth and color. See Bulletin 504 for a listing of insecticides registered for borer protection.
NOTE: Disclaimer - This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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