Today, I released a bunch of wasps into a forest in Wisconsin…
Now tell me what sort of image does that conjure up in your head?
Well, if you’re of my generation (mid-twenties), it might consist of something looking like the image on the left (Beedrill, for those of you not baptized into the church of Pokemon as children, as I was), multiplied into a swarm of sorts, as the bottom image shows. While this prospect may seem terrifying/exciting/(insert adjective here), I’m going to break it down for you, I did not release a swarm of Beedrill (is that the plural? Beedrill…Beedrills…? I know, I’m too tangentially worried about Pokemon.) into a nearby forest. I apologize to any enthusiast who was hoping his or her dream may have come true. Sorry.
To move back in the direction of more seriousness, you may wonder why I felt it necessary to go into that whole bit about the Beedrill and wanting to catch all the Pokemon. I must digress. Many of our perceptions are shaped by the things in which we most commonly associate them. When I mentioned “wasps,” you certainly may have thought about Beedrill, or “killer” bees (even though they aren’t wasps), or a recent SyFy original movie. I wish to dispel that notion and enlighten you a little bit (if I may).
Although we are correct when we call this (Paper wasps, Polistes spp.), and this (Digger wasp, Philanthus sp.), and this (Sapygid wasp, Eusapyga verticalis), wasps, they are by far the “only” wasps. In fact, the family Braconidae is one of the largest, most highly diverse, family of wasps, with estimates from 50,000 to 150,000 species living today. One may be incredulous at such a claim, but it is in fact true. Many of these wasps, especially those that parasitize other organisms, can be very cryptic, or difficult to discern against the background of the outdoors. Additionally those that are parasitic (termed, parasitoids), spend the bulk of their life cycles inside other organisms, hiding them from only those that know where to look.
If you’re still with me at this point, you’ll notice I’ve highlighted a few things:
(1) I released wasps into a Wisconsin forest
(2) Wasps are a diverse group and
(3) We should not immediately associate the term “wasp” with something that is negative to, or will attack humans
Now that I’ve gotten you (hopefully) to reassess your predisposition to cringe (or run and hide), when you hear someone say, “wasp” (and if you already knew all of this stuff, pat yourself on the back and forgive my slow synthesis), I’d like to introduce you the two wasps that I released into the forest today.
The first image on the right is of Spathius agrili, a parasitoid of the Emerald ash borer (Agrilus planipennis) from China. Although the picture may make it seem rather large and menacing, it’s actually quite small and docile. To get a good (general) comparison of the size, take one of your hands and look at your pinky nail; the wasp is slightly smaller than that. This wasp, being a parasitioid has two goals in life (if I may be so bold and anthropomorphize it): first, to mate, secondly, to find the Emerald ash borer’s larval stage, and lay its eggs on it. A parasitoid that lays its eggs on an external surface of a larvae is known as an ecto-parasitoid. In the case of this parasitoid (as well as many others that are ecto-parasitioids-but remember there are always exceptions), it is also known as an idiobiont, which is a parasitoid that paralyzes its host after oviposition-preventing it from moving further. This makes perfect sense- if a parasitoid lays its eggs on the outside of its host, it does not want the host to be able to move and potentially crush or defend itself against the Spathius agrili larvae consuming it.
The second image to the right is another parasitoid from China that lays its eggs in the Emerald ash borer, Tetrastichus planipennisi. This wasp is even smaller than S. agrili, averaging the size of a grain of rice. Unlike S. agrili, T. planipennisi is an endoparasitoid, meaning it lays its eggs inside of the larvae, rather than externally. Because this wasp does not lay its eggs on the outside of the larvae, it has no reason to paralyze it and prevent it from moving. In fact, the host larvae will continue to feed (and therefore provide nutrition to the eggs and T. planipennisi larvae) until the eggs inside it hatch and consume its innards. Parasitoids that employ this non-paralysis strategy are known as koinobionts.
What do you notice about these two parasitoids?
Probably that they have two pointy things that look a lot like stingers. Let me clarify, those are not stingers. We are looking at two females both of which have a organ called an ovipositor. What this organ does is allow a female to direct where she lays eggs. In the case of these two wasps, they both use it to probe the wood of ash trees until they find an Emerald ash borer larvae, in which they then, lay their eggs. Let me emphasize again, they is an organ to lay eggs; not sting things.
Another thing you may have noticed, is that unlike the Emerald ash borer, these wasps do not have common names, only scientific ones. This is a result of them being cryptic (as I mentioned above). These insects were not named as species (giving them formal scientific recognition) until they were found on a survey that specifically looked for natural enemies (I defined this in my previous post, “In search of native Agrilus…”) of Emerald ash borer. This further emphasizes that this insects are harmless to humans- if it doesn’t sting or bite or provide something beneficial, it can go unnoticed.
The purpose of this post was to introduce you to the wasps that I released today and quell the misconception that every wasp is a bad wasp. What I will do in the second part of this series is introduce you to the Emerald ash borer and explain why wasps from China are being imported into North America to attack (lay their eggs in) it.