Overwintering Cocoons and Pupae

by Robert Jindra

Sphinx kalmiae larva, courtesy of Robert Jindra

In late summer of 2005 I had the pleasure of meeting Robert Jindra of Germany (residence close to Nuremberg in Bavaria). Robert was visiting his parents who were vacationing in Cape Breton, Nova Scotia.

Robert travelled to Montague, Prince Edward Island, and had a tour of my rearing operation. Robert has extensive experience rearing Sphingidae in Germany and has also reared some Saturniidae.

Robert writes, "I had great success with my kalmiae-rearing. They are now all pupated. I want to show you a picture from a very fat larva and a kalmiae pupa, which has pupated in a hollow of a humid sand-soil mixture. I made this image with my brand new digi-cam 'Sony Cybershot DSC-H1'.

"I also want to show you one of my special boxes to overwinter my pupae/cocoons. This box has a bowl on the bottom with some water inside. Inside, in the middle there is a gauze-frame with two linen-towels, where the pupae/cocoons lie in between. If the temperature is above zero, the bowl should be filled with water. So the linen is able to absorb the humidity. During the winter time, when the temperature falls below zero, the bowl should be empty.

This box has also some round holes covered with gauze (for mouse-protection!) near the bottom for air-circulation. With this box I never had any problems to overwinter the pupae/cocoons."

Robert adds an interestng technique to delay the emergence of caterpillars from eggs:

"I fortunately was lucky with my cooled Sphinx poecilia and Sphinx kalmiae eggs in the fridge. I had a nearly 100% hatch rate. I took the eggs overnight into the fridge by level 2 (approximately 8 Degree) and I took them into our basement by approximately 15 Degree during the day. So I delayed the incubation-time almost to 100% without any losses.

"I fed the kalmiae caterpillars on Ligustrum ovalifolium (California pivet). Spirea and privet twigs are perfect for watering!"

Below is a picture of a Sphinx kalmiae pupa, reared from eggs whose incubation had been delayed by almost ten days via chilling method described above.

Robert has also passed on some information about his observations of Sphinx kalmiae pupae.

"In Germany I place the “earth”-caterpillars which are ready to pupate into big plastic containers with approximately 30cm deep soil. I use soil with a very soft riddled (without crumbles) mixture of 50% sand and 50% clay. The soil should be humid but not wet. The caterpillars dig into the soil down to approximately 20 cm below surface and then they make an egg-shaped hollow. Some species cover the hollow with some silk-strings too. Because of the perfect moisture into the hollow, the caterpillars will turn into a perfect pupae with an extremely smooth skin.

"After the caterpillar has turned into a pupa, it will stay in the hollow until eclosion. The pupa definitely does not wiggle to the surface! The full developed moths of the earth pupators are always hatching out in their hollows. Just after they have eclosed, they dig to the surface, probably with using the old tube of the caterpillar. "

I asked Jim Tuttle for his eclosion experience with earth pupators and he writes (August 28, 2005), "As for the pupal emergence, it has been my experience with Manduca sexta and Citheronia regalis that the pupa works its way to the surface (head up), stops just as the head breaks the surface of the ground, and then the adult breaks out of the pupal shell.

"I can only assume that the pupa is using the same path that was previously dug by the larva. I dug emergence pits in my yard, let larva burrow in, let the pupae naturely overwinter, and then monitored the subsequent emergences.

"I cannot speak to any other species... I do know that I decided to take this observation approach because I felt that any observations in artificial containers might taint the results or my perception of the process.

"Is it possible that the adults of some species eclose in the subterranean chambers and then make their way to the surface - I guess so..."

Robert adds, "I can remember when I was twelve years old. I reared some caterpillars from Laothoe populi. It was my first experience with rearing caterpillars. After the grown caterpillars left their stems, I took them into a plastic container with a sand/soil mixture. After fourteen days I took the pupae out of their deep hollows and was waiting and waiting for their eclosion, but nothing happened. (at this time I knew nothing about diapause). I took them back into the earth-container.

"After one or two days I saw more and more pupae appearing right on the surface with their heads up. They indeed wiggled to the surface because I destroyed their hollows. An adult moth cannot emerge when the pupa is enclosed by earth. Wiggling up to the surface probably is an emergency procedure if the hollows get destroyed. But I have to admit, that S. kalmiae caterpillars are making not very stabile hollows in comparison to S. ligustri or A. atropos. So I guess in nature it happens very often that the hollows of some “earth-pupator species” get destroyed."

For the last several years I have been using a soil-less pupation method for Sphingidae and Ceratocampinae. I have often felt the "barbs" and cremasters of many such pupae were used to help them wiggle to surface prior to eclosion. Perhaps some species wiggle to the surface and others eclose in their subterranean chambers. I have not had problems with naked pupae emerging from uncovered storage conditions in plastic tubs.

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