Pesky Parasitoids, Part 3

First, another quick update on the leafminer book. Some people have asked if there’s a way to get it without recurring monthly payments, and/or by writing a check rather than going through Patreon. At the same time, Patreon recently announced that they’re about to start adding a service fee to every pledge. So I’ve come up with some new options, which you can check out on this page (scroll past the picture of the moth to see them). Anyone who has already signed up through Patreon is welcome to switch at any time, or to stay there if you’re happy with it.

And now for a little break from leafminers…  In our surveys on Nantucket, Julia and I have started to branch out to looking for other obscure herbivorous insects rather than just gallmakers and leafminers, with the thought that we’ll eventually stop finding new galls and leaf mines. Some of the things we’ve been focusing on lately have been micro-moth larvae that fold, roll, and tie leaves. On July 30, while walking around Stump Pond, we noticed a patch of bugleweed (Lamiaceae: Lycopus uniflorus) in which many of the leaves were curled downward laterally and nibbled toward the tips. These three photos are different views of the same leaf:

In that last photo, you can see that there’s a tube of silk within the leaf curl. Here’s a better look at one on another leaf:

There was a caterpillar in each leaf curl, but they all zipped back into the safety of their silk tubes before I could get any photos of them. We collected several to try and rear, but within five days, braconid wasp larvae started emerging from them—all of them—and spinning cocoons. At least braconids don’t devour their hosts very thoroughly, so I have a photo of a recently abandoned corpse that gives some idea of what the caterpillars looked like.

On August 15, an adult microgastrine braconid emerged from one of the cocoons. Note the neat circular lid it cut from the end of the cocoon when it emerged.

There were four other cocoons, but nothing else emerged until September 5. Then, over the next week, these little cuties emerged from three of the cocoons:

Unlike the braconid, they emerged through ragged holes in the cocoons:

These wasps belong to a species of Perilampus (Perilampidae), and they are obligate hyperparasitoids with an unusual way of locating their hosts. Instead of seeking out a suitable host larva in which to oviposit, the female lays her eggs on leaves. It is then up to the newly hatched larvae to wander in search of a parasitized caterpillar, burrow into it, locate the parasitoid larva (which might be a wasp or a tachinid fly), and burrow into that. The Perilampus larvae in my bugleweed caterpillars bided their time while the braconid larvae finished feeding and popped out and spun their cocoons; then they got around to devouring the braconid larvae or pupae, at which point they conveniently had ready-made cocoons in which to pupate. It all seems very improbable, but I guess it works for them!

Edit, 1/23/2018: I sent these specimens to perilampid specialist Chris Darling, and he says:

I have had a look at your specimens and they fit nicely into my concept of Perilampus platigaster Say, 1836.  But yours is the best rearing record we have for this species.  Specimens have been reared from the grape leaf roller, Desmia funeralis, but the details of the association, and the primary parasitoid, were not available or not recorded.  And your rearing information agrees very well with the numerous host records that Dan Janzen has for this species group from Costa Rica.

Your account of the biology of Perilampus [above] is quite good.  But I would note that not all species are hypers.  And as far as we know the planidia do not search for parasitized caterpillars — but rather the planidia enter the caterpillars before they are parasitized.  And they only develop if the caterpillar is subsequently parasitized, which makes the life history all that more bizarre.  Planidia show up in genitalia preparations of moths occasionally, so they entered the caterpillar and were marooned when the caterpillar was not parasitized and subsequently metamorphosed into an adult!

And I am sure you will keep an eye out for Perilampus next summer!  Perhaps you will find them ovipositing on bugleweed near leaf rolls.  Sadly, they do not appear to parasitize  leafminers!  Almost certainly the mines provide protection against the tiny marauding planidia.

Here is an example of a planidium that Terry Harrison found while dissecting a moth.