Hackberry psyllids in homes

These nipple-like galls on hackberry leaves protect a small
insect called Pachypsylla. In the fall the insects emerge and
may invade nearby structures.

Insect species that specialise in invading homes in the fall are almost as predictable as the cooler weather itself. A number of insect species, like paper wasps, multicolored Asian lady beetles, box elder bugs and cluster flies are already pretty well known to the pest control industry. But nature is full of surprises, and there's always an obscure insect or two that can surprise you.

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

This year seems to have been a good year for one tiny invader, at least in the north Texas area. It's the hackberry nipplegall maker, Pachypsylla celtidismamma.  If you've ever noticed nipple-like swellings on hackberry leaves, you already know a little about this insect. Pachypsylla is a genus of homopterous insects in a family referred to as psyllids (SILL ids).  The specialised Pachypsylla grows up only inside galls that form on hackberry leaves.  Like other gall makers, 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 fastidious homemakers, or the unprepared PMP, 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).  This week I've had multiple reports of Pachypsylla home invasions here in north Texas.  Most calls are accompanied by deep concern by homeowners that these tiny insects might be harmful.

You can tell your customers that hackberry nipple-gall insects are pretty harmless.  They do not bite and do not eat clothes (and don't hog the remote!). Apart from needing to be vacuumed up from windowsills occasionally, these insects shouldn't pose too much of a problem; however I suggest an application of a pyrethroid insecticide to the outside frames of windows and doors.

These insects are small. Adults are 2-3 mm-long (about 1/8-inch) and just a little over 0.5 mm wide. With the average window screen mesh about 1.5 mm apart, these guys can easily slip through screens. Recommend to your client to check the tightness of seals around windows and doorways, the most common points of entry.

If Pachypsylla invasions are a regular occurrence at an account, suggest that the property owner remove nearby hackberries and replace them with another well-adapted tree.

According to the Encyclopedia of Insects, the exact mechanism by which insects induce plants to form galls is still poorly understood, but it involves chemicals applied to or injected into the plant that influences plant growth hormones.  In the case of Pachypsylla, the plant responds to its springtime egg laying by forming  round, nipple-like galls on the undersides of developing leaves.  Each gall surrounds a growing Pachypsylla nymph.  In the fall mature adults emerge from these galls and search for a protected site to spend the winter. There is only one generation per year.