Monthly Archives: November 2016

Cottonwood Gall Aphids (Pemphigus populitranversus)

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Pemphigus popilitranversus


Cottonwood Gall

While I was raking leaves off our small “lawn,” my wife (knowing full well the answer would be yes) asked me if I wanted to see a leaf gall. It was formed on the petiole of an Eastern Cottonwood (Populus deltoides). I checked bugguide.net and identified that a Cottonwood Gall Aphid caused the gall.  Poplar Petiole Gall Aphid is another common name for this species.

Pemphigus popilitranversus

Cottonwood Gall                  Left hand gall showing transverse split

It is a hollow gall, not quite round, with a transverse split. It occurs along the petiole (the stem of a leaf) just below the blade. I cut a few open and found a waxy substance but no insects. They might have exited through the slit. I opened one more and found the adult aphid.

Pemphigus popilitranversus

Interior of Cottonwood Gall    L – shed skin                 R – adult winged aphid

I Googled the scientific name and the phrase “life cycle” and found Roberta Gibson’s informative and fun blog “Growing with Science (The Poplar Petiole Gall Aphid was the “Bug of the Week” in May of 2015.) She explains the aphid’s life cycle. Aphids seldom have straight forward life cycles. They over winter as eggs on Cottonwood twigs. They hatch in the spring and feed on the leaf petioles, causing the plant to produce the gall. Then the insect moves inside. It becomes a winged adult and exits through the slot in the gall’s side. They complete their life cycle on the roots of cabbage, turnips, or another member of the mustard family (Brassicaceae). Another common name is Cabbage Root Aphid. The aphids complete their life cycle by flying back to Cottonwoods and depositing eggs on the twigs or bark.

This is a great time of year to look for galls. Get outside and enjoy Nature. Also, check out Roberta’s blog and website. Even though she is based out of Arizona many things she writes about occur in Michigan.
Copyright 2016 by Donald Drife

Webpage Michigan Nature Guy
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Don’t Touch That Beetle: Oil Beetle (Meloe sp.)

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meloe-sp-oil-beetle-1During a recent work session at the Royal Oak Arboretum one of the Boy Scouts found a large purplish-black beetle. It was part of the Blister Beetle group called an Oil Beetle (Meloe sp.). They exude an yellowish oily substance from the base of their legs that forms blisters if it contacts human skin. They placed the beetle in a large plastic cup and the cup’s bottom was spotted with oily liquid when I first saw it.

This genus consists of six species in the Northeastern United States. I am not sure which species this one is. I am happy to know the genus of an insect.

Meloe sp.

Female Oil Beetle

The females are about twice the size of the males. This female was 40mm [1.5 inches] long and seemed sluggish. They overwinter as eggs and perhaps she had laid her eggs and was reaching the end of her life. This is a flightless, parasitic beetle. The eggs hatch in the late spring and the larva are described as alligator-like. Climbing onto a flower they wait for one of the solitary bees to land and quickly latch on to its back. The Oil Beetle larva rides the bee back to its nest and feeds on the developing bee larva and possibly some of the pollen in the nest. It then pupates and emerges in the fall to mate and lay its eggs.

It is fun to find a new insect in an area that I visit often. You never know what you are going to see when you just get out and look.
Copyright 2016 by Donald Drife

Webpage Michigan Nature Guy
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