Cecropia Caterpillars Enter Apolysis For Fourth Instar (6/25-6/26)

Our oldest three third instar Cecropia caterpillars (Hyalophora cecropia) have entered apolysis.

---

6/26:

Today we checked on the Cecropia caterpillars frequently, hoping that one of the three caterpillars that entered apolysis yesterday would ecdyse, but none of them did. The apolysis period takes a longer time every instar so this isn't too surprising, but they will surely molt tomorrow. We made sure too get some better pics of the caterpillars in apolysis as seen above. Their entire bodies are now extremely tight and swollen, which is especially apparent in the third photo. Fourth instar must have a huge cuticle compared to third instar's and it is getting really stuffy in there. Here are the numbers for today; two more thirds entered apolysis
Count: L3+: 5; L3: 28; L2+: 1; dead: 2 (drowned)

6/25:

Today our oldest three third instar Cecropia caterpillars entered apolysis for the fourth instar-but let's start from the beginning first. At around 4:00-4:30 PM, we checked on the caterpillars and noticed the oldest individuals were all extremely plump with tight looking cuticles. Looking closer, we saw that the bases of their tubercles were swollen as seen in the three photos below. It is most apparent with the red tubercles because of the contrast on the green but all the tubercles appear to be swollen under close inspection. The swelling is due to the much larger fourth instar tubercles already taking form underneath the current cuticle and it should probably intensify as it gets closer to ecdysing into fourth instar. Also, we suspected the individual on apple on the right-most photo was already in apolysis because it had created a silk pad (look closely at the picture) and was very still which are early signs of apolysis despite that the head capsule has not shifted yet.  

At around 7:00-8:00 PM, we checked on the caterpillars again, and found that three caterpillars had displaced head capsules, two of which are the ones shown in the photos above (left and middle are same individual on plum, right is a different individual on apple), so our apolysis suspicions were correct. Below shows an up close head and full body photo of the individual on plum from above left and middle photos. If you look at the close up head photo, you can clearly see the displaced head capsule as well as the swollen red tubercles, especially at the bases. The cuticle of the whole body in general is very tight as well.

​Other than this plum feeder individual in the photos, the other two caterpillars in apolysis are both apple feeders, which is quite surprising since last time around during the second to third instar molts, the plum feeder ecdysed a whole day before the two apple feeders but this time around the apple feeders caught up (or the plum feeder slowed down?). We think this is possibly because the apple leaves are a better food choice for indoor rearing (we do not know about outdoors or in the wild), because the leaves are bigger and provide more living space, and seem to retain water slightly better than plum leaves. 

Anyway, below are the numbers for today. We expect the three caterpillars in apolysis to molt tomorrow night or the day after.
Count: L3+: 3; L3: 30; L2+: 1; dead: 2 (drowned)

- Alan