Hackberry nipplewhat?

This week has been the week of the hackberry nipplegall maker, Pachypsylla celtidismamma. I should have known when, during the Entomological Society of America's annual conference in Austin last week, I opened my 23rd floor hotel room blinds and saw the outside window covered with these insects.

Pachypsylla adults (about 1/8-inch long) are
commonly found at this time of year indoors, around windows

Sure enough upon return to my office, calls and messages were awaiting me about little "gnats"  covering window screens, outside walls, and cars. The small size of these insects allows them to enter buildings with ease, even squeezing through window screens.  Though these insects are present annually, the invasion seems to be unusually heavy and widespread this year with complaints from Austin to east Texas and the Dallas area.

Pachypsylla is a genus of tiny insects that grow up inside galls that form on hackberry leaves. Also called psyllids (SILL ids), they are not gnats or flies, but belong to the same order as the leafhoppers and cicadas. Like other gall making insects, Pachypsylla adults lay their eggs on leaves, which then start to swell around the egg or developing larva, forming a gall. After feeding on the gall tissue all summer, Pachypsylla adults emerge in the fall. Unfortunately for your customers, these adults commonly enter structures at this time in their search for a warm place to hang out and, perhaps, catch some football or prime time TV during the winter.

The nipple-like swellings on hackberry leaves give this little
insect its name.

Despite being a nuisance, hackberry nipple-gall insects are pretty harmless.  They do not bite, do not eat clothes and do not hog the remote. Apart from needing to be vacuumed up from windowsills occasionally, there is little you can do about these insects. In most cases, poor seals around windows and doors provide entry points, but truth is they can get indoors through any crack or gap in the building envelope.

Those who have tried spraying window screens with an insecticide noted that the main result is smeared windows.  If you do offer to spray, keep your sprays limited to window and door frames, and obvious gaps and cracks in outdoor siding.  I do not advise treating indoors, as these insects should die relatively quickly anyway. And no, you can't treat the trees. A vacuum is the best control tool, in my estimation.

For customers who find the invasion to be an annual occurrence, removing nearby hackberry trees and replacing them with another well-adapted tree is one possible solution.  Keep in mind, however, that these little guys can fly.  They were, after all on my 23rd floor windows  last week. So if other hackberries are nearby, cutting down the tree may not help a lot,  especially during a banner year like this.

I have no explanation for the great numbers of nipplegall makers this year.  This obscure group of insects has not been as well scrutinized as other, more important pests.  However we do know there was something they liked about 2013, rain at the right times, the temperature, or few natural enemies.