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.

The Standard Bearer – Ensign Wasp

An ensign wasp (Evaniidae) perched on a wall.

Due to their long legs and antennae, an ensign wasp on a wall may resemble a spider from a distance, and like spiders, they ought to be welcome guests in a home.  These little wasps are unable to sting and harmless to humans, but they are deadly to roaches.  Like many other small wasps, ensign wasps are parasitoids:  the female ensign wasp lays her eggs only in the egg cases of cockroaches, where the larvae hatch and quickly devour the cockroach eggs.

Ensign wasps (also called hatchet wasps) are members of the family Evaniidae, and take their common name from the distinctive shape of their gaster (rear end).  It is flattened laterally, and attached high like a flag.  Much like a banner waver, they will twitch their gaster rapidly up and down when disturbed.  The species I find around here is also notable for the attractive blue eyes that can be seen under a hand lens.  They main body is perhaps 1cm long, with the legs and antennae nearly doubling the size.  I found the wasp pictured above hanging around in the hallways of our building on campus, defending us from roaches.