Disease Strikes the Pipevine Swallowtails

Today when we checked on our California Pipevine Swallowtail newborns (Battus philenor hirsuta), we were devastated to discover what we believe is a mysterious disease has struck our caterpillars.

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For over a week since we first obtained our first newborn Pipevine Swallowtail colonies they looked absolutely great. They would feed gregariously side by side in perfect parallel rows with their heads aligned in the same direction or rest together in little clumps. For such little guys, each colony ate and pooped a lot since there were so many of them in each one. 

Starting on Thursday 6/28, we had witnessed disease spreading among our Cecropia (Hyalophora cecropia) and Ceanothus (Hyalophora euryalus) caterpillars. Whether or not the disease was related in any way or not between the two species, they were both hit at the same time, the Cecropia caterpillars right after the Ceanothus. Symptoms were similar in that the infected caterpillars would very abrubtly lose their appetite and wander aimlessly for days before becoming weak and starving to death. Molting caterpillars could be infected too and would mismolt due to weakness. With the potential annihilation of our entire stock of these caterpillars, we took some pretty serious measures to try to contain the disease. For one thing, we moved all of the Cecropia into outdoor rearing sleeves away from the site of the pathogen and sterilized all potentially contaminated rearing enclosures with bleach. All dead or sick caterpillars were removed immediately for both Cecropia and Ceanothus. 

At first, we thought that these actions could contain whatever disease(s) was/were infecting our Cecropia and Ceanothus caterpillars and at very least stop it from spreading to another species since we are keeping so many caterpillars right now. However, just yesterday we realized that at least one of our Pipevine colonies was not acting right. The suspect colony was fairly large and consisted of all first instar caterpillars that were in apolysis for second instar. At first, it was impossibly difficult to tell whether they had been infected by any disease because during this state the caterpillars are fairly immobile, weak, and loose their appetite -- all of which are possible symptoms of disease -- anyway. But after two days without any of the caterpillars molting yet, it was pretty clear that something was up. 

Today when we checked on these guys, they still had not molted and many of the caterpillars had seemed to become so weak that they had lost their grip. Their prolegs had begun to shrink in and they were unable to cling onto the leaf properly let alone perform the molt. It created a sort of scattered look with caterpillars lying around in random positions rather than clumped compactly as they should be. Within a few hours most of the caterpillars seemed dead and we threw the entire petri dish along with them into the trash. When we looked at our other colonies, it appeared that the dish directly under this one had also been infected and were very near death. That one also went into the trash.

Whether or not the disease from the Cecropia or Ceanothus caterpillars are related to each other or even related to what we were witnessing with our Pipevines is impossible to tell. But in any case, we were not willing to take the risk and decided that anything that had any contact with any of the three species was in high risk for contamination. We decided to completely evacuate all of our Pipevine newborns into a different room away from the site of the disease and then buy some new plastic rearing containers at night to replace the current ones. 

When we came back from buying ten new containers that night we realized another Pipevine colony was in danger. Like the first colony, the caterpillars were all in apolysis for second instar and two of its members were already dead -- very limp, without a trace of life left in them. At this point, we were quite scared and decided to take measures even further. We decided to separate the rest of the presumably healthy colonies into groups of 4-6 in order to prevent total death of the colony should even one individual within it contracts the disease and spreads it within the dish. Each of the groups were moved into completely new, sterile petri dishes, putting on a new set of gloves for each dish we changed to prevent spread of the pathogen. Each dish was given new leaf cuttings from the middle of our leaf bag since the outer leaves had less of a chance of being contaminated through handling. Finally, we moved all petri dishes into yet another new room and spread them out so that none were touching. We bleached or threw away any potentially infected items in the trash can outside such as used petri dishes, containers, leaves, and gloves. 

This is the first time we have encountered such a disease crisis and we hope that we are dealing with it appropriately. If there are more dead colonies by tomorrow, we will most likely have to destroy our entire stock and start over fresh in order to get rid of the disease. 

- Brian