Monday, February 20, 2017

A caterpillar green around the gills, part three

The wasp pupae did not look particularly remarkable, but inside a rapid transformation was taking place. In just one week, the wasps emerged as adults.

The newly emerged wasps gathering on the lid of the vial.
They were, of course, still just as small. Nevertheless, looking closely, it is possible to see that there were two types of wasps. While some of the wasps had typical antennae, the antennae of the other wasps were branched, giving the appearance of delicate antlers.

A view of the wasps from underneath.
The two types of wasps did not mean that the caterpillar host had been parasitized by two different species, however. The two types were males and females. As in some other insects (for example this moth and this mosquito), the more elaborate antennae belonged to the males.

The wasps likely belong to the tribe Eulophini in the family Eulophidae.
Finally, it was time for the wasps to go off in search of their next hosts -- though the one pictured above spent some time inspecting my hand before disappearing into the air.

Monday, January 30, 2017

A caterpillar green around the gills, part two

After emerging from their caterpillar host, the young wasps quickly lost their plump, bright green forms.

Day 1: The wasp larvae (right) emerge from the moth caterpillar (left).
Over the next two days, they first faded to a dull yellow...

Day 2: The wasp larvae begin to pupate.
...and then shriveled and blackened.

Day 3: The wasp larvae have become pupae.

However, the wasps were not sickening and dying -- they were progressing normally through their development from larvae to pupae. Meanwhile, the moth caterpillar that stood by, apparently healthy except for its inertia, had its own development frozen. To be continued...

Friday, October 30, 2015

A caterpillar green around the gills, part one

This Halloween, instead of featuring a seasonable insect or spider, I will share a spooky story of a "possessed" caterpillar.

Parasitoids may be among the smaller enemies that a caterpillar has, but they are also among the most insidious.  When a female parasitoid (generally a small wasp or fly) finds a suitable caterpillar, it lays its eggs on or even inside the caterpillar.  The parasitoid larvae then emerge from the eggs and proceed to feed on the caterpillar.  What becomes of the caterpillar once the parasitoid invasion is complete?  It may be mummified, vanish from inside a fuzzy shroud, or perhaps more strangely -- be left apparently unharmed.

A copper underwing (Amphipyra pyramidoides) caterpillar and recently emerged parasitoid wasp larvae.
The light green caterpillar shown above and below is surrounded by the darker green larvae of a parasitoid wasp.  The wasp larvae had recently finished feeding inside the caterpillar and had broken through the sides of the caterpillar to finish their development outside.

The slits that the wasp larvae emerged through are visible behind them.
Meanwhile, the caterpillar just sat there as if unperturbed by the litter of parasitoids.

However, the caterpillar was hardly passive.  When the parasitoid larvae were threatened by an approaching object, the caterpillar became surprisingly aggressive.

The parasitoids had left the caterpillar alive, but not at liberty.  Though the caterpillar was no longer needed as food, it could still be manipulated into serving as the parasitoids' protector.

To be continued... but in the meantime, you can explore some more: Parasitoid Increases Survival of Its Pupae by Inducing Hosts to Fight Predators