Hackberry Psyllids: A Fixture of Fall

Sometimes, it is easier to identify an insect by the evidence it creates than by seeing the bug itself. Such is the case with the abundant, but tiny, hackberry psyllids, genus Pachypsylla in the family Psyllidae and true bug order Hemiptera. Psyllids are also known as "jumping plant lice" for their resemblance to aphids and ability to vault themselves away from danger.

Along one of the streets that borders our townhouse complex in Colorado Springs are a pair of hackberry trees, among the few planted ornamentals that are not oak, maple, or elm. They are invariably exploited every summer by Pachypsylla celtidismama, which produces "nipple galls" on the underside of hackberry leaves. The small, tumor-like growths do not seem to affect the health of the tree in the least, but provide housing and food for the tiny insect within each one. Up to 52 galls have been found on a single leaf (Caldwell, 1938), and they vary from smooth in texture to rather hairy. Double and triple galls are not unheard of, but it is rare to find more than one nymph occupying each gall.

The adult stage of hackberry psyllids will start appearing shortly, if they are not emerging already. Adults of P. celtidismama are only 3.5-4.5 millimeters in length from "nose" to the tips of the folded wings. They resemble tiny cicadas, but can also be confused with barklice, order Psocodea. Barklice have chewing mouthparts, though, while psyllids in general have beak-like piercing-sucking mouthparts they use to tap plant sap.

Hackberry psyllids make themselves a real nuisance when they start seeking nooks and crannies in which to hibernate. They can gather by the dozens, if not hundreds, on the exterior of doors, window screens, and the siding of homes. They pose no threat, of course, and simply hosing down the masses with water will solve the problem. The appearance of these insects en masse is a brief affair anyway.

A different Pachypsylla species

Next spring, female psyllids will deposit eggs on the leaves of hackberries at the precise time when the leaves begin unfolding from the bud. Should a psyllid deposit her eggs too early, or too late, and the chances of successful development of her offspring plunges dramatically.

The formation of the bulging gall is the tree's response to the feeding of the nymph that hatches from the egg. The little dome-like pocket insulates the nymph from hostile abiotic environmental factors, and protects it from at least some predators and parasites. The nymph goes through five stages, the last instar illustrated in the images below. Note the two pairs of developing wing pads. The spike-like projections on the rear of the insect will help it to cut an exit in the gall before it emerges as an adult.

Nymph of P. celtidismama © Hannah Nendick-Mason via Bugguide.net

Nymph of P. celtidismama © Hannah Nendick-Mason via Bugguide.net

Despite their seemingly impenetrable fortress, the nymphs are still vulnerable to tiny parasitic wasps, including Psyllaephagus spp. (family Encyrtidae), and Torymus spp. (family Torymidae). The larval wasps feed as parasites on the nymphs and then chew their way out of the gall once they complete development.

Psyllaephagus sp. © John Rosenfeld via Bugguide.net

This, and the other six species of hackberry psyllids, range pretty much wherever hackberry occurs naturally, and increasingly where it is used as an ornamental tree. The different species of psyllids make correspondingly different styles of galls, so it is easiest to assess the gall shape, size, and location to determine which psyllid is responsible. Keep in mind that gall midges (family Cecidomyiidae) can also create galls on hackberry.

You might try rearing a few galls to see what parasites emerge along with the adult psyllids. It is entirely possible you could record a new host record in the process.

Sources: Berenbaum, May R. 1989. Ninety-nine Gnats, Nits, and Nibblers. Urbana: University of Illinois Press. 263 pp.
Caldwell, John S. 1938. "The Jumping Plant-lice of Ohio," Ohio Biological Survey Bulletin 34, vol. VI, No. 5: 229-281.
Winterringer, Glen S. 1961. "Some Plant Galls of Illilnois," Story of Illinois Series No. 12. Urbana: Illinois State Museum. 51 pp.

Pumpkin Bugs

This year I actually carved a jack-o’-lantern for the first time in decades. My landlady had purchased several pumpkins and then had a carving party on Saturday, October 24. Since I’m a football fan, and I’m in New England, I carved mine in the form of a Patriots helmet. It turned out pretty well, and I had fun doing it. Once we set the hollow gourds out on the porch, though, insects began flocking to the fermenting fruits. By Halloween day, a surprising variety of critters could be found outside and inside the pumpkins.

October 31 was an unseasonably balmy day here in South Deerfield, which probably had a lot to do with the buzzing insect population. Among the more interesting visitors was this little “jumping plant louse,” in the family Psyllidae. Psyllids are related to aphids, and a few can be pests in their own right. They are quite tiny, but under magnification can be quite colorful and lovely as well.

The psyllid’s kin, aphids, were also out and about, drifting on the wind and alighting wherever their feet found purchase. This is the time of year when aphids are winged, seeking the alternate host plants where they will overwinter. While some species pass the cold months as adult insects, the majority probably lie dormant in the egg stage.

Not surprisingly, flies made up the bulk of the visitors to our big orange globes. Fruit is fruit, and even if the inside of a jack-o’-lantern must seem like a domed stadium to “fruit flies,” they treated it like a bunch of overripe bananas, carrying on their courtship dances and lapping up the liquid residue. These are actually “pomace flies” or “vinegar flies” in the family Drosophilidae, and not true fruit flies (those are in the family Tephritidae and they attack fresh fruit, wreaking economic havoc on growers). The adult female pomace fly lays her eggs in the decaying fruit and the larvae that hatch feed mostly on the yeast that is carrying out the fermentation process. The maggots can really hold their liquor and quickly mature in the alcoholic mess.

Larger flies were to be found as well, including vivid metallic “green bottle” blow flies in the family Calliphoridae, and flies from the family Muscidae (house flies and kin) were chief among them. Oddly, even this parasitic fly of the family Tachinidae visited. Tachinids are, as larvae, mostly internal parasites of other insects. Some tachinids are very “host specific,” meaning they attack only a handful of host insects, often caterpillars. Other species are “generalists,” and just about any old caterpillar will do. It is essentially impossible to identify tachinids beyond the family level unless you are an expert specializing in that incredibly diverse family.

Maybe my favorite fly of the day was this pumpkin-orange Homoneura fly in the family Lauxaniidae. You can see more detailed images of these little beauties on the Bug Guide page for the genus.

I can’t think of a better way to share a pumpkin than with the insect world. While we humans admire the glowing spheres cut in familiar, humorous, or scary patterns, the insects remind us that there really is such a thing as reincarnation, if not in spirits, then in the molecule-by-molecule recycling of pumpkin flesh into fly flesh. I, for one, kind of like that idea.