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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Unbelievable Insect Numbers, Part I

This article was published originally on 5/18/1994
The combination of weather we experienced last summer, fall and winter has put us in a position this spring to witness emergence of unbelievable numbers of pine bark adelgids (also known as pine bark aphids). This is the insect characteristically known for causing trunks of heavily infested pine trees to appear white (as if painted). These adelgids have a fuzzy white covering similar to mealybugs and large populations can completely cover and obscure the bark. Pine bark adelgids are found on the bark of the tree trunk and larger branches, though they are also common on the bark of twigs, at the base of the needles. The aphids are sap feeders and suck sap from the phloem, through the bark.

Observations reported this spring mention a pile of tiny insects 4 to 6 inches deep at the base of the tree. Some people have insisted upon calling them tiny black spiders. The size of these newly emerged adelgids is about 1/16th inch. A 4 to 6-inch deep ring of tiny insects around a 12-inch diameter tree must amount to millions and millions of nymphs, an indication of how successful this species was on the infested trees last summer. Most observations so far have involved very large, mature trees.

Adult female adelgids spend the winter on the trees and begin producing eggs in the early spring. These hatch into the tiny nymphs that are quite mobile and move about the tree searching for a feeding site. Apparently, large numbers also fall or crawl from the tree and collect on the ground around the base.

Damage to healthy, well established pine trees is not common, though small, newly transplanted or otherwise stressed trees may suffer from heavy infestations. The nymphs on the ground are of no danger to people, pets or other plants, and most will probably starve or be eaten rather than successfully establish on the tree. Populations vary considerably from year to year, apparently in response to weather and predator activity.

What this means is that if the tree is otherwise healthy, spraying now is not necessary, and that populations may decline on their own. Trees of the age and size indicated are not likely to be greatly affected by this pest. I suggest giving the trees TLC to avoid any further stress and watching to see if the population increases.

Chemical control of the adelgids is available if needed. The time to spray is either early spring (before bud break) with oil spray, or in mid-May with oil, soap, malathion, Orthene or diazinon. Spray the bark of the trunk and major branches according to label directions. Masses of tiny nymphs on the ground around the base of the tree can also be sprayed.



This article originally appeared in the May 18, 1994 issue, p. 75.

Year of Publication: 
1994
Issue: 
IC-467(12) -- May 18, 1994