A few weeks ago we met the boxwood leafminer (April 23, 2007), a strange fly that infests the leaves of boxwoods giving it a case of the blues. This week I passed a large American boxwood with a different set of the blues. Most of its terminals were severely deformed. Instead of beautiful broad lanceolate leaves, this one's leaves were misshapen and curled into tight cups at the branches' ends. On closer inspection, small filaments of white wax were visible inside the cupped leaves. Attached to the wax where small pale green insects. These were the immature stages, nymphs, of the boxwood psyllid (pronounced "sillid").
A quartet of psyllid nymphs happily hunker in a cupped leaf sucking sap and making wax.
Psyllids are another insect that gives boxwoods the blues each spring. Boxwood psyllids have siphon-like mouthparts and are relatives of other suckers such as aphids and cicadas. They feed by inserting their piercing beak into the vascular tissue of the plant and withdrawing nutrient laden sap. The curious curled wax filaments produced by the nymphs can exceed the length of the psyllid's body. The wax is thought to provide protection from other insects that might find these tender nymphs a tasty meal. Several weeks ago nymphs hatched from tiny eggs hidden beneath the scales of the boxwood buds. These eggs were inserted into buds by adult psyllids that made boxwood their home last summer. Over the next several weeks, nymphs will complete development and shed their skin one last time to become adults.
A young psyllid adult rests after escaping from the skin it wore as a nymph. See the wax on the shed skin.
Adult psyllids closely resemble miniature versions of cicadas that visit us in the late summer and autumn. Adult psyllids also have sucking mouthparts and feed for several weeks on the boxwoods before laying their eggs in terminal buds. Only a single generation of psyllids occurs on boxwood each year. Adult psyllids are also known as jumping plant lice and they will be with us and our boxwoods for the remainder of May and well into June. They are easily detected by running your hand through the foliage of the boxwood. If present, they will jump off the shrub and fly about in astonishing numbers. I have read accounts of people being bitten by adult boxwood psyllids, but I cannot imagine the bite to be anything memorable or remarkable. Even though the boxwood psyllid causes a brief case of the blues, most boxwoods appear to simply outgrow the damage. Chemical or psychological therapy is usually unnecessary and, in time, the boxwoods get over their blues with little permanent damage.
References
For more information on boxwood psyllids, please visit the following websites.
http://www.hgic.umd.edu/_media/documents/hg52_000.pdf
http://www.umassgreeninfo.org/fact_sheets/piercing_sucking/boxwood_psyllid.html