Sunday, 27 November 2016

When will my moths emerge?

Apparently one of the most frequently asked questions when breeding silkmoths.  It is also one of the most difficult to answer.

In most parts of the world, apart from the wet tropics, a caterpillar’s food plant is actively growing and available for only part of the year.  As a result, many species of butterfly and moth have needed to develop some strategy to avoid having their caterpillars hatch in the middle of winter, or during a long, dry season.  One of the ways they can do this is for the pupae to go into diapause -  its a dormant stage, a bit like hibernation. 

So here is the dilemma with my  Samia cocoons  -  they are a cross between ricini and walkeri.  Now walkeri is the race that has been introduced into Italy and parts of the USA, and has successfully managed to survive in the wild there for many, many years.  It is able to do this because the pupae go into diapause and remain inside the cocoon over the winter, only completing their development and emerging when spring temperatures are warm enough.   But that’s not the whole story, because some moths are multibrooded - if the growing season is a long one, then the first batch of caterpillars produced might pupate quite early in the summer, and instead of going into diapause, the moths might emerge within a couple of weeks and produce a second generation of caterpillars that will pupate at the end of the summer, with these later individuals overwintering.   So walkeri pupae might go into diapause, but ricini are very different. 

Samia ricini are tropical and their life cycle is a continuous one, going from egg to caterpillar, to pupae, to moth, then pairing, laying eggs and the whole process continues.  It doesn’t give you much of a break when you are rearing them  -  in reality, by the time the last caterpillar has pupated, the first moths may well be emerging, ready to pair and lay eggs that will hatch a couple of weeks later.  It can become a bit of a chore and more than a little inconvenient if you want to go on holiday  - have you ever tried to get a petsitter for your caterpillars?

So there you are, when will my moths emerge?  Will they go into diapause?  Its just a matter of wait and see for now.  They are in the emerging cage, keeping warm for the moment.
I have some different cocoons that are in diapause.  These ones are Antheraea mylitta, the Tussah Silkmoth, producer of tussah silk.

These are tropical moths so they don’t want a cold winter, they are instead going through their dry season.  I am keeping them at room temperature, and then if all goes according to plan, in the spring I will put them somewhere warmer, in an enclosed cage with damp moss on the bottom, and mist them.  As long as it stays warm and humid, this will mimic monsoon conditions and encourage them to emerge.  Timing is important though, because once they emerge and pair, the eggs that they lay will hatch in another couple of weeks and by that time, I will need to have a supply of fresh oak leaves for the caterpillars to eat. 


The cocoons of mylitta are quite big, and they are really hard.  Its quite hard to believe that they will really break down into a mass of soft, silky fibres.    

With some cocoons it is possible to carefully cut them open and look at the pupae to check that they are still alive, and whether they are in diapause or forming up ready to emerge.  Its not recommended with these cocoons though, its too likely that you would damage the pupae by trying to open them, as well as making it very difficult for the moth to successfully emerge from the cocoon later on.  I am hoping that these are all still alive and will emerge at the right time, but there is never a guarantee.

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