Honeylocust is one of our finest native shade trees. It is widely used in urban plantings by virtue of its ability to tolerate or even thrive in the hot, dry, and polluted environs of cities. Originally from the lowlands of the Mississippi and Ohio River valleys, honeylocust is now widely planted throughout North America. Each spring a withering plague hits the honeylocusts planted in residential landscapes and corporate campuses round about the communities of central Maryland. The withering begins almost as soon as the new leaves begin to unfurl. Tiny leaflets that should expand to small ellipses crinkle, twist, and cup until the entire leaf is stunted and deformed. Some of the leaves remain with the tree for the duration of the growing season. Others are dropped and will be replaced with a second crop if damage is quite severe. The culprit behind this plague is a tiny sucking insect known as the honeylocust plant bug.
Amazing that one so tiny can cause so much damage.
Plant bugs are sucking insects with the type of beak described in our friend, the wheel bug (see "It's the Wheel Thing, Assassin Bug", Bug of the Week, (LINK TO) August 1, 2005). Unlike assassin bugs, the honeylocust plant bug is not a meat eater. It is a plant eater and uses its beak to pierce the tender cells of expanding plant leaves. It sucks the contents of the cells destroying tissue and the ability of the leaves to expand normally. The resultant injury leaves the foliage of honeylocust shriveled and deformed.
A pair of plant bug nymphs cavort on a twig.
By this time in June, most of the small, wingless nymphs of the honeylocust plant bug have completed their juvenile growth and molted into winged plant bug adults. A vigorous shake of a branch can send dozens of these bright green bugs into swirling flight. Adults also suck the life from leaves further exacerbating the destructing caused by the nymphs.
Tucked inside a branch these eggs will hatch next spring.
Adults mate and, using a bayonet-like appendage called an ovipositor, insert dozens of eggs just beneath the surface of the 2 to 3 year old twigs. These eggs will weather the heat of summer and cold of winter to hatch next spring when buds break on honeylocust and new leaves appear. While the damage to honeylocust may be nasty especially early in the spring, this honey is one tough tree and a flush of new leaves in June and July often hides the damage. Some entomologists recommend a well directed wash with a stream of water to dislodge the nymphs and knock them to the ground where predators await to gobble them. There are also several insecticides available to kill plant bugs, if damage is severe and one is so inclined. I just wait. Honeylocust has a much more challenging nemesis to face. One we will visit in a future Bug of the Week.
References
For more information on honeylocust and its plant bug, please visit the following web sites.
http://www.na.fs.fed.us/pubs/silvics_manual/volume_2/gleditsia/triacanthos.htm
http://www.ext.colostate.edu/PUBS/insect/05571.html
http://www.uvm.edu/extension/publications/el/el150.htm