Pipevine Chrysalises and the Chalcid Wasps

As the days past, we are discovering that more and more of our wild-caught Pipevine Swallowtail chrysalises (Battus philenor) had been parasitized by chalcid wasps (Brachymeria ovata). 

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Anybody who has ever collected caterpillars or chrysalises from the wild has probably encountered a number of parasitoids. It is a risk we all have to take because you never know their there until its too late!

Starting on 6/26, we first noticed that two of our Pipevine Swallowtail (Battus philenor) chrysalises -- one directly wild-caught and the other from a fifth instar caterpillar that had been wild-caught -- had started developing strange red splotches on them. At the time, we were unsure whether this was normal or not since it was our first time really seeing Pipevine Swallowtail chrysalises at all. But what was alarming was that the red splotches were not symmetrical. Moreover, it also didn't make any sense that they would appear on some chrysalises and not others and that they showed up randomly and not immediately after the chrysalises had completely hardened after pupation. For example, the wild-caught one had clearly pupated for several days before we collected it because it was completely hardened (a process that takes at least two days) while the other one developed the spots immediately following pupation. 

In a few days, we confirmed our suspicions on 6/28 that something was up with these two chrysalises, as well as a with a third wild-caught one we found that day. The truth was, all three of the chrysalises seemed quite dead at that point so we thought it would okay to just pierce one open and investigate. Upon making an incision in the first wild-caught chrysalis with a pointy toothpick, we discovered that the chrysalis was, indeed, very much dead and hollowed out (eaten) by a very large parasitoid maggot. We later identified this as a species of chalcid wasp, specifically Brachymeria ovata. In the end, this was not a big surprise. I mean what else could have killed them besides simply drying out? 

In the past few days we are beginning to discover that many more of our recent chrysalises have been parasitized. Almost half of them at this point are highly suspect. Just like any other species of caterpillar, the Pipevine Swallowtails have their own natural enemies. Unlike most caterpillars, they don't have to worry about external predation because they are protected by their toxic aristolochic acids; parisitism is actually their biggest problem. The vast majority of the parasitized chrysalises have been undersized; none of the healthy ones are undersized. In hindsight, we were probably wrong about there being such a massive size variation in these species. Then again, the smaller ones do tend to be eaten alive faster and therefore show the red splotches much faster (some of the big chrysalises that seem healthy may still eventually turn out parasitized).

Luckily, we didn't actually have too many caterpillars/chrysalises that were wild-caught. The bulk of our stock right now comes from the 200+ eggs we have collected so hopefully all of the surviving members from these groups are totally fine. 

- Brian