Rearing notes for western tiger swallowtail (Papilio rutulus) pupae. Stock originated from a single pairing between reared female and wild male in Albany, California, Summer 2017; currently in third generation.​​​​

We have taken pupae of Papilio glaucus, Papilio rutulus, and Papilio zelicaon, and cocoons of Hyalophora cecropia and Callosamia promethea out of the refrigerator to break diapause as the growing season begins.

Earlier in January of this year, we put all of our pupae from last summer's rearings in the refrigerator at 5° C  for them to overwinter. Now that the weather is becoming consistently warm (20+ °C) and the leaves beginning, we decided to some of the species out to break diapause.

After a chaotic week of flight delays due to snow storms on the East Coast, we have finally made our way from California back to Ithaca. Since a sustained period of cold is necessary for most diapausing pupae to break diapause in the spring, we placed two airtight plastic boxes full of pupae from our last summer's rearings into the refrigerator, set to 5° C. Ideally we would have done this much earlier (probably in October when it starts getting chilly outside), but since the dorms require us to unplug refrigerators over Winter Break, we decided to wait until after we came back. Hopefully, the 3-4 months in the refrigerator will be sufficient enough for the pupae to undergo a normal diapause (assuming we take them out in May). 

The species overwintering are as follows (locality/date stock originated): Papilio glaucus (New York 2018), Papilio rutulus (California 2017), Papilio zelicaon (California 2017), Hyalophora cecropia (New York 2016), Callosamia promethea (New York 2018), Antheraea polyphemus (New York 2018), Darapsa myron (New York 2018), Hemaris diffinis (New York 2018), and Paonias myops (New York 2018).  

Also included were our batch of northern walkingstick (Diapheromera femorata) eggs from last fall. We are unsure of the conditions required for these eggs to undergo normal diapause and break it, but assume it follows the same principle as lepidopteran pupae.

Alas, the list of pupae is much shorter than we had hoped, since many of the species we reared last summer never entered diapaused and the stock was lost (Papilio troilus, Papilio cresphontes, Actias luna, Pachysphinx modesta, Eumorpha pandora, to name a few...). Nonetheless, we are grateful for the species that did make it and look forward to rearing them again this summer.

​Brian Liang 
Brian Liang is a student at Cornell University in Ithaca, New York pursuing an undergraduate degree in entomology. He is co-owner and a main contributor of the Liang Insects blog, insects articles, and site design.

This is the sixth day since the first eggs were laid by one or both of the rutulus (Papilio rutulus) females we hand-paired using a climate chamber, popup cage, and willow (Salix) cuttings. Sixteen of what was originally about 90 of these eggs hatched today. A few of the newborns are shown below, some having already fed on fresh willow in water tubes. We plan to rear them in aluminum foil pie pans, which are roomy and much cheaper than plastic containers of the same size, with paper towels to suck up moisture and promote better ventilation. 

We are unsure whether we should be excited or disappointed at this initial turnout. Over the course of their development, an alarming percentage of the eggs dessicated and collapsed. Virtually all of the eggs that had fallen off the willow leaves or were never laid there in the first place dessicated and many of the eggs that developed to the black stage did not hatch. At one point, it seemed doubtful that any sort of substantial amount would hatch at all but 16 is not a bad start. The reason behind the poor hatch rate is unknown. For one, it is uncertain whether desiccation caused the death of the egg or if the eggs died for another reason and then dessicated. The detached eggs likely dessicated but at the same time, eggs that are attached to plant material can also be prone to dessication because the dried leaf material can draw water out of the egg. The death of the misshapen eggs is not too surprising either, but it is strange that there would be these misshapen eggs in the first place. We have never seen anything like this in the wild or in our own breeding of swallowtails. The deformity probably comes as a result of the egg being laid sideways and not setting correctly as a result when the shell is still soft.  Granted, it is quite strange that the butterflies would lay the eggs sideways, even if the cuttings were awkwardly positioned.

The degradation of the plant material with the eggs could have also caused harm by way of certain microbial organisms. But perhaps one of the most likely causes of egg mortality could have been excessive heat. We did not remove the eggs until a day or two after they were laid in the climate chamber, which could approach 29°C. Outside the climate chamber, indoor temperatures are also quite high. Swallowtail eggs, which have delicate translucent shells, are extremely sensitive to heat, especially when not protected by living plant material. Even if eggs develop, by the time the larva is ready to crawl out, it may be too weak due to loss of body fluid and resources to hatch properly, analogous to dead adult in pupae syndrome. 

On the bright side, we do have 16 healthy neonates and it does look like a few more might hatch.