Jeff Hahn, Assistant Extension Entomologist Adelgids are very close relatives of aphids. Like aphids, they are small, soft-bodied insects with piercing-sucking mouthparts. The differ from true aphids by lacking cornicles (small tailpipe-like appendages on the abdomen) and having generally shorter antennae. Many adelgid species commonly produce tufts of whitish, waxy material. Heavy infestations can make trunks and branches look like they have been flocked. All adelgids feed on conifers.
A common species in Minnesota is the pine bark adelgid, Pineus strobi. They prefer white pine but are also known to occasionally feed as Scotch and Austrian pine. These small (1/32 inch long), dark-colored insects spend the winter as immature females. When temperatures warm to about 50 degrees F in the spring, they become active and produce large amounts of white, waxy material which covers their bodies. The immature adelgids finish developing and turn into adults. This generally occurs sometime during late April in Minnesota.
The females lay eggs which hatch into small crawlers. Most are wingless but a few possess wings. They disperse and eventually settle down and attach themselves on the tree. They are commonly found on the trunk and underside of branches as well as smaller twigs and new growth. They insert their stylet mouthparts into the bark and feed on sap from the phloem tissue. Crawlers develop into immature adelgids which are incapable of moving. Eventually they mature into adults and repeat the cycle. There can be as many as five generations a year.
Pine bark adelgids cause little injury to healthy, mature trees, especially when only light or moderate numbers are present. Natural control by several predators, especially lady beetles and syrphid fly larvae, help keep adelgid numbers down. Even when infestations are so heavy that trunks or branches to appear to be white, very little harm is being inflicted on the trees. However, it is possible that young or unhealthy trees can be damaged by large populations of pine bark adelgids. Their feeding could result in discolored or distorted foliage, reduced plant growth or even (under extreme conditions) death.
Infestations by these adelgids usually affect just the tree's appearance, especially if they are on a vigorously growing, well-established pine. In most cases, just ignore the pine bark adelgids that you find. If you have trees that need to be protected, e.g. recently transplanted or unhealthy trees, first try to knock the adelgids off with a hard spray of water. If this is not sufficient, try dormant oil, applied during early spring before new growth emerges.
It is possible to apply a residual insecticide, such as acephate, during the spring or summer, although this should only be done with great reservation. There should be obvious risk to the tree's health due to adelgid feeding to justify such action. Keep in mind that the same insecticides that help manage adelgids would also kill their natural control agents. This could ultimately make the adelgid problem worse. Insecticidal soap is an alternative to residual products. It is much easier on insect predators but it may not be as effective on the adelgids.
