I’m finally getting back to working on my guide to sawfly larvae, after a very busy field season followed by several weeks of focusing on writing papers—some of which have involved documenting new host records and previously undescribed sawfly larvae, so in that way I’ve already been making some progress this fall. This week I’ve started to tackle the chapter on conifer-feeding sawflies, and this morning while taking a break from that and sorting through some of my photos from this past June, I coincidentally came across some relevant photos that I couldn’t resist sharing here.
On September 20, 2020, I led one of my only public walks of the year, during which the group encountered some red-headed pine sawfly larvae (Diprionidae: Neodiprion lecontei) chomping on pitch pine needles (Pinaceae: Pinus rigida). I didn’t have any photos of this species yet, so I took three home to photograph them:
They exhibited their charming behavior of standing up and blowing bubbles when disturbed:
Now that I had these larvae I figured I might as well rear them to adults, so I kept them in a jar with some soil in the bottom and two days later they shed their skins…
…and now they were prepupae, done feeding and ready to burrow down and spin cocoons. The prepupa of this species looks much like the feeding-stage larva but its head is no longer red.
Between June 27 and July 5 of this year, three adults emerged from those three cocoons, but as in my previous “Sawfly Surprise” post, they were parasitoids rather than the sawflies I was expecting. Last time the wasps were eulophids, which is the #1 family of parasitoids I get when trying to rear leafminers, but this time they were perilampids. I’ve just encountered perilampids once before, when three adults of Perilampus platigaster emerged from cocoons of braconid wasp larvae that had emerged from some caterpillars that remain unidentified because every last one of them was parasitized. These new perilampids, which Jeong Yoo tells me are P. hyalinus, have the same adorable general appearance as P. platigaster but with the added bonus of being shiny blue and green.
I presume the above wasp is the male, and the one below (more blue, with larger abdomen) is the female.
In my previous Perilampus post I described the life cycle of perilampids that are obligate hyperparasitoids, entering caterpillars with the hope of finding primary parasitoids to parasitize. It turns out that P. hyalinus is sometimes a hyperparasitoid, e.g. emerging from puparia of tachinid flies or cocoons of ichneumon wasps that are formed within the cocoons of Neodiprion sawflies, but normally when it attacks Neodiprion sawflies it feeds as a primary parasitoid. Tripp (1962)* studied this relationship in great detail and reported that P. hyalinus females lay eggs at the bases of pine needles four to six inches away from groups of second-instar Neodiprion larvae. Why? Because it takes the eggs eight to ten days to hatch, and that’s how long it takes the young sawfly larvae to move about four inches along the stem—and there are nine days between molts, so the sawfly larvae will be in their third instar when they arrive near the eggs. Neodiprion larvae that are fourth instar or older cover much more ground and would just blow past the eggs before they hatched. Why not just lay eggs directly on the sawfly larvae? Well, before the eggs hatched the larvae would shed their skins, so that wouldn’t work out. Maybe by now they could have evolved eggs that hatch more quickly, but with the current arrangement they get to avoid that flailing, bubble-blowing behavior shown above. The fluid that comes out of the larva’s mouth is sticky and could cause major problems for a tiny parasitoid that came in contact with it.
So, the P. hyalinus larvae hatch shortly before the arrival of their slow-moving hosts, and they stand erect on the pine needles until the sawfly larvae blunder into them. Each P. hyalinus larva clings to the surface of its host for less than an hour, and then burrows inside and basically does nothing until the following spring. When the weather warms up and the Neodiprion larva starts to prepare to pupate, the P. hyalinus larva pops back out of it and feeds on it externally (but inside the cocoon), quickly paralyzing it and then devouring it over the next two weeks. It then pupates without spinning its own cocoon, and after another two weeks it emerges as an adult and chews its way out of the sawfly’s cocoon.
If I’d had to guess what series of events had led to these little blue-green wasps emerging from the soil into which my sawfly larvae had burrowed nine months earlier, I don’t know what I would have come up with but it certainly wouldn’t have been that! I’m so grateful for everyone who has taken the time to figure these things out and publish them so that curious naturalists, decades or centuries later, are able to find answers in a matter of minutes instead of having to start from scratch.
* Tripp, H. A. 1962. The biology of Perilampus hyalinus Say (Hymenoptera: Perilampidae), a primary parasite of Neodiprion swainei Midd. (Hymenoptera: Diprionidae) in Quebec, with descriptions of the egg and larval stages. The Canadian Entomologist 94: 1250-1270.