We Have to go Deeper

A mass of yellow cocoons attached to the end of a twig.

Hi!  It’s been a few weeks, hasn’t it?  I have all these pictures and draft posts but no time to finish any of them because I am trying to get my analyses done for the ecology conference this August.  I am tragically productive.

Here are some cocoons I found up at the Oklahoma biostation back in spring.  Cocoons are awesome because they are basically insects you can rear without actually doing any work.  I stuck these guys in a jar for a week or two to see what would emerge.  What I got was tons of tiny black and brown wasps.  I took some pictures under a scope and threw them up on BugGuide where I they were quickly ID’ed by the excellent Bob Carlson.  BugGuide is awesome, because it is basically network of experts you can access without actually doing any work.

A female braconid wasp (Cotesia), emerged from the cocoons.

The black wasps turned out to be members of the genus Cotesia, in the family Braconidae.  These are parasitoid wasps which lay their eggs on (or in) caterpillar hosts.  The larvae develop inside the caterpillars Alien-style, slowly eating them alive, before eventually emerging to pupate and seek out new hosts.

A female ichneumonid wasp (Mesochorus) emerged from the cocoons.

The brown wasps turned out to be a species of Mesochorus which are hyperparasitoids of the original black wasps.  These are parasitoids of parasitoids which lay their eggs in the egg or early instar larvae of the Cotesia parasitoid wasp as it develops in the caterpillar host.  (Read that sentence back to yourself until it makes sense.)  If this arrangement seems unnecessarily complex to you, just realize that hyper-hyperparasitoids also exist.  Every “hyper” kicks it down another level.  It’s basically the plot of “Inception” but with innards-devouring bugs instead of dreams.  (“Insection“?)

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.

Aliens

Parasitoid wasps parasitize an insect egg case.

Found these tiny wasps parasitizing a mantis egg case or ootheca in Argentina.  You can see the tiny wasps rearing up and inserting their long ovipositors.  In higher members of the order Hymenoptera, the female ovipositor is modified into the sting (only female bees, wasps, and ants can sting.)

‘Parasitoids’ are distinguished from ‘parasites’ in several ways.  A parasitoid insect lays one or multiple young on or into a single host organism–often a juvenile or egg.  The young develop inside the host, which may live on for some time, but almost always ultimately succumbs to the creature devouring it from the inside out.  Anyone who has watched the movie Aliens may find this sequence of events familiar.  Parasitoids thus are not true parasites as they kill their host, but not quite predators, in that they consume only one prey item during the course of their lifespan.