I’m calling these potato monsters

Gall aphid colony in pecan leaf.

I wrote this post up back in the spring, then accidentally deleted it and was too disheartened to come back to it for months.  But these little guys are too cool to abandon forever.  The little yellow potato monsters in the photo above are pecan gall phylloxera, a relative of aphids and thrips.  They are exceedingly tiny.  So tiny that although I observed and curiously popped open the large pecan leaf galls many times while rearing my lunas, it wasn’t until I idly took a look under a scope one day that I even realized the little insects were there.

Open and closed pecan leaf galls with gall phylloxera colony.

Pecan phylloxera have fascinating, complex life cycles.  These vary quite a bit between species, but I’ll share a general example, that of Phylloxera devastatrix, probably the most damaging pecan phylloxera.  Pecan phylloxera galls are started by “stem mothers,” who inject a toxin into the plant while feeding on young tissue.  This toxin stimulates the plant to grow a gall, gradually encasing the feeding insect over the course of several days.  Each stem mother then lays eggs in her gall, which develop and feed in relative safety.  In late summer, at the end of the gall’s life cycle, the galls split open, allowing winged asexual phylloxera to disperse.  They’re not done yet.

Close up of pecan gall phylloxera and eggs.

Not content with such a simplistic, multigenerational life cycle of barely three tiers, the asexual phylloxera find a good spot and lay some eggs.  Two different sizes, just to be more special.  The large eggs hatch into sexual females, and the small eggs into sexual males.  The phylloxera mate, and the mamas-to-be seek out a nice sheltered place…where they die.  This gives the eggs a nice, cozy refuge to ride out the winter–tucked up safe in mom’s dead body.  In the spring, the eggs hatch out of their mother and become stem mothers, which disperse to find young plant tissue and start new galls, beginning the beautiful cycle of life once again.

Damn, I love nature.

More pictures:

Gall phylloxera and eggs in an opened pecan leaf gall.

Close up of pecan leaf gall phylloxera.

Underside and mouthparts of pecan gall phylloxera.

Pecan gall phylloxera nymphs are exceedingly tiny.

References:

Phylloxera gall on Pecan, TAMU

Pecan Phylloxera, Smith & O’Day

Pecan Phylloxera, OK State

The Mummy – Aphids and Parasitoid Wasps

The remains of a parastized aphid ("mummy") complete with parasitoid escape hatch.

My labmate Collin found mummies in his aphid colony.  It was kind of exciting, although maybe not up to horror movie standards.  Mummies are what happen to aphids when a parasitic wasp injects them with an egg.  As the wasp larva grows inside their bodies, feeding on their hosts, the still living aphids swell into pale, bloated, unmoving forms on the leaf surface.  Eventually, adult wasps burst from their hosts, leaving behind the kind of gruesome sight pictured above.

Close up of cotton aphid (Aphis gossypii) feeding on a cotton leaf.

For comparative purposes, here are pictures of a healthy, live aphid, as well as the shed skin of an aphid following a molt.  For a frame of reference these guys are about a millimeter or two long.

Cotton aphid exuvia (cast off exoskelton) on a cotton leaf.

Special thanks to Collin McMichael for helping me with the digital microscope photography.  And thanks also to someone who featured a how to on manual focus stacking in photoshop a while back.  I cannot find this post again for the life of me.  There was a picture of an ant with a parasitoid I think.  It was awesome.  I have been wanting to try this technique for a while, so it was fun to experiment.  I should probably get a shot with the legs in better focus in the future.

At the Aphid Bar

Sugar ant (Brachymyrmex) tending aphids on flower bud.

As mentioned in a previous post, many phloem-feeding hemipterans, such as aphids, take in excess sugar, which they excrete as a substance called honeydew.  This sugary substance attracts other sugar feeding insects, which has led to some interesting interactions.  Among the most notable is the development of a mutualistic, or symbiotic, relationship between some ants and aphids.  Ants may ‘tend’ aphids, drinking the honeydew and protecting the aphids from predators in return.  This provides the additional benefit to the aphid of preventing the build up of their sugary excrement which could encourage the growth of fungi and mold.

Carpenter ants (Camponotus) tending aphids. A parasitic wasp perches on the edge of the leaf.

Ant-hemipteran interactions can be observed almost anywhere if one takes the time to observe closely.  I found the carpenter ants above tending aphids on the bushes right outside my front door.

Of course, as in any biological relationship, cheaters exist.  Some ants tend aphids without providing any protection against predators.  Some aphids manufacture less nutritious honeydew.  On the other hand, some ants take their care of aphids to extremes, even building structures to protect the aphids against winter cold.

Silhouette of carpenter ant tending aphids.

Sunny Suckers

Aphids nestle under the base of a flower in Sam Houston National Forest.

Anyone who has spent much time around plants will be familiar with this classic gardener’s pest, the aphid.  Aphids use their piercing-sucking mouthparts (a characteristic of the order Hemiptera)  to drink the fluids of plants.  Fluid uptake occurs passively via the pressure generated by the plant’s own circulatory system.  In fact, the aphid’s mouthparts actually contain valves to limit the flow.  Without such systems the aphid would literally be blown off the plant.  It is more the equivalent of attempting to drink from a firehose than sucking from a straw.

Aphids are gregarious insects which live in small subsocial colonies on plants.  Reproduction varies among aphid species and may be sexual or asexual.  Many aphid species give live birth to young.  In the picture above and below, a few white and shriveled cast off exoskeletons are visible from developing aphids.  These skins, called exuvia, can become quite numerous as colonies grow and become crowded.  Overcrowding on plants generally triggers the production of winged aphids, which disperse to new host plants where they found new colonies.

Aphids coat a plant stem in Argentina.

Minute Monster – the immature ladybug

Baby lady beetles munching aphids.

Another picture from right in my backyard!  Unlike their pretty and popular adult form, ladybug larvae look a bit like they ought to be featuring as monsters in a horror movie, and they are indeed fearsome predators.  (At least of the very tiny.)  But just like grown up ladybugs these strange critters are the gardener’s friend, since their favorite prey are aphids.  Another trait they have in common with adult lady beetles is their bright coloration.  This aposematic, or warning, coloration serves to alert predators that they are not good to eat, due to the toxic chemicals they sequester in their bodies.

Lady beetles belong to the family Coccinellidae, which takes it name from the word coccus, meaning circular, due to the adult beetle’s nearly circular shape.  They are also generally almost flat on the bottom, allowing them to draw their legs under their armored exoskeleton and fit almost perfectly against a plant surface when under attack.