Devastating Disease Outbreak in Ceanothus and Cecropia Caterpillars

Today when we checked on our Ceanothus (Hyalophora euryalus) and Cecropia (Hyalophora cecropia) caterpillars, we were absolutely devastated to discover that several caterpillars from both species appeared to be sick with a disease, the first major caterpillar disease outbreak we have had in years.

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For the past few weeks up until now, both our Cecropia and Ceanothus caterpillars looked healthy and strong, with only three accidental deaths since hatching. The Cecropias are just now molting into fourth instar while the Ceanothus are now molting in third; so far, so good. However, today when we checked on them in the morning, we found two Ceanothus caterpillars dead and a very sick looking Cecropia caterpillar as there was no evidence of feeding from it (no hole in the leaf in its immediate vicinity) and its body looked limp and weak. In addition, several other Cecropia and maybe a few Ceanothus caterpillars didn't seem quite right either and seemed to have eaten less than usual.

We quickly removed all sick looking individuals from their containers and disinfected all six Ceanothus containers and the Cecropia container that contained the sick individual with bleach. We then gave all the healthy looking Ceanothus caterpillars new leaves and made sure to wear a new set of gloves for each container to minimize cross contamination. For the sick individuals, we put them each in a different plastic cup with a petri dish lid and gave them a fresh leaf, though it is unlikely they will eat it. 

We are now very worried for both our Ceanothus and Cecropia caterpillars because we had small cultures of both to begin with (36 Cecropias and 24 Ceanothus), and we can not obtain more of either of them in the wild here in Albany. For years we have never had a serious disease problem with our caterpillars, except for the year of 2013 with the Anise Swallowtail caterpillars.

To admit, however, over the years we have primarily reared butterfly species and only dabbled with Saturniidae because there are very few species from this family hear in Albany (and Western North America in general; the vast majority reside in Eastern North America), and the few species that are apparently here are rare. Thus, this disease outbreak is likely a result of our inexperience with rearing Saturniidae species. Most guides for rearing Saturniidae recommend sleaving tree branches for outdoor rearing or closed (air-tight) containers for indoor rearing. As we do not have Ceanothus caterpillar host plants in our yard and were afraid that outdoor rearing would dehydrate the Cecropia caterpillars because the California summer climate is much drier than most of their natural range, we chose indoor rearing for both species. However, indoor rearing has a much higher risk of disease than outdoor rearing, especially with air-tight containers because there is no ventilation. The purpose of closed containers is to keep the humidity high so that the caterpillars won't desiccate, but this sacrifices ventilation and increases the chance for disease greatly (high humidity + no ventilation = perfect environment for pathogens). We are almost certain that these factors played at least some part in creating the disease outbreak, and air-tight containers was our biggest mistake. Nothing else could have played a very significant role in instigating disease because the food was always kept very fresh (water tubes and changed everyday), and the frass was changed everyday which should be adequate enough in maintaining good sanitation. We do not even know if the disease started in the Ceanothus caterpillars or the Cecropias, or if the two outbreaks are even related, but we suspect it began with the Ceanothus since two were already dead when we checked compared to one sick Cecropia. Also, Ceanothus caterpillars are native to California which has a much drier summer climate than the habitat of most other Saturniids, so an air-tight container with high humidity may have been a serious mistake (we did not know if this was the right thing to do because there's almost no information out there at all on rearing this specific species). Species that normally reside in drier environments generally would have the highest disease risk in a humid one because they are not accustomed to it.

In either case, we have learned our lesson now and will try to get all the healthy Cecropias onto live host plants as soon as we figure out how to create rearing sleaves from mesh screening. For the Ceanothus we might consider buying a live plant from a nursery or simply take them out of the closed containers and raise them on cuttings in the open room.

Update: Here of some pictures of the sick caterpillars that eventually died on 6/30. The left shows a third instar Cecropia caterpillar in apolysis that turned brown and flaccid, unable to carry through with its molt. The right photo is of a second instar Ceanothus caterpillar that lost its appetite and eventually shriveled up and died in a pool of orange-brown fluid. Several other caterpillars have died since as will.

- Alan