Lately I’ve taken to getting backlit shots of leaf mines by removing one of the Twin Lite flash heads and holding the leaf on top of it, so that when the flash goes off the mine is illuminated from both sides. This allows me to get a detailed look at what is going on inside the mines, and recently I’ve spotted a few parasitoid wasp larvae by doing this.
Here is a shot I took of an agromyzid fly mine (Phytomyza sp.) in an aster leaf (Symphyotrichum sp.) collected in Ohio. In ambient light, I couldn’t quite tell whether the fly larva was still inside or not.
Looking at the end of the mine, I saw that something was amiss.
At the very end of the mine (to the left in the photo above), you can see the shriveled remains of the fly larva. To the right, there are three little greenish wasp larvae that have wandered a short distance back down the mine. I took those photos on September 28, and from October 10 to 16, three of these little wasps emerged:
They are about 1.5 mm long and are some type of eulophid, but not one of the kinds I commonly get from leaf mines.
On October 9, I picked up a recently fallen red oak (Quercus rubra) leaf containing a number of tiny Bucculatrix leaf mines.
Taking a closer look at the mine above, I saw that the moth larva was still inside–and that there was a wasp larva feeding inside it.
The moth larva’s head is pointed down, in the lower right corner of the photo. Along the upper edge of the wasp larva, you can see several little pseudo-legs, reminiscent of the ichneumon wasp larva in this post. Based on that, I suspect this is the larva of a wasp in the related family Braconidae, which is the main type of parasitoid that emerges from leaf mines other than Eulophidae. In another post, I showed a braconid that emerged from a Bucculatrix larva that had been parasitized after emerging from its leaf mine.
For more fun with parasites, check out the new National Geographic cover story by Carl Zimmer.