Why do pupae turn?

I can't remember where I read this, or if this applies to all Heterocera, but it has to do with orientation with respect to light/the sun.

I think you are probably right Bill. It is one of my favourite books and I had a hunch that's where I read it, but I just wasn't sure. The book has so much first hand rearing information it's incredible. I think it's out of print now though.

The information pointed to sounds intuitive, but I wouldn't trust it to cover the entirety of the behaviour; or to put it another way, it might not be that simple. Though I am judging from ignorance since I can't check the reference and see how much it goes into the subject.

Thanks for the reference.

@ eurytides

What is the pupation period of your A. polyphemus individuals, if you've reared them before? I'm waiting on a few S. pyri (the ones I hear rustling, now less) and they are two days away from reaching a month, I'm not used to such a long period; though I imagine it the regular for saturniids.

Indeed, the species is univoltine. But the eggs provided were not F0; meaning, they were out of their usual time for occurrence. The first larva pupated almost a month ago, but in the wild the adults would have been on the wing until recently, perhaps some still are. So, by this, the pupae I have should eclose to be part of the univoltine cycle, that is: to mate, lay eggs, and have larvae grow until the end of Summer, when they will pupate and then settle to overwinter.

I really assumed this to be the case, that is, that this time-lag would allow adults to somewhat cheat on the regular cycle... am I completely off track?

I see the reasoning. But now I have trouble with causation: do the pupae enter diapause and remain in so until temperatures drop and then rise (like what general fruit trees go through, e.g. Prunus)? Or do they enter diapause because the temperature is low?

Off the hat, I have this to support the latter: Many overwinter two or more times, particularly if the springs are cold. Source.

Thanks Adam. I hope someone can contribute a bit to this.

From first hand experience I know that all that has been written about diapause and the need for cold temperatures is not uniformly true, even in the highly respected reference books.

Typically here on PEI in eastern Canada where polyphemus are normally single brooded, I will sometimes see a very small (less than 1%) of cocoons that I have harvested (sometimes several thousand harvested cocoons in a single year) in August-September even into October will yield moths that same year even though there would be no hope of a second brood successfully maturing before the cold weather sets in. Moths were emerging in August through early October indoors in very small numbers.

I have taken polyphemus adults at lights here as late as July 10 (female) which is typically too late for a second brood to mature from her offspring. Peak flight is normally early June to late June.

I grew up in New Jersey where there would be one, usually two, and sometimes a partial third brood of polyphemus, seemingly depending upon local conditions of temperature. If we had a warm early spring, and summer was hot, there would be at least a partial third brood. If there was a late, cold spring, followed by a cool summer, there might only be a single brood.

I rear lots of Hyalophora cecropia and H. Columbia Columbia here every year. Many years ago I reared a good number of cecropia indoors. One mature larva did not spin amongst the foliage but somehow mananaged to spin a cocoon beneath the baseboard hot water radiation cover. The cocoon remained there undetected throughout the fall and winter and emerged in early May. I assume its emergence was probably governed by an internal clock and probably by light photo period. Occasionally I have read from what seem to be quite reliable references that cecropia in very small percentages will attempt a second brood. I think this may happen in some of the southern states where larvae and cocoons may experience a similar photo period length in the increasing hours of daylight in the spring and decreasing hours in the fall. Perhaps if the larvae or pupae experience the same photo period length in the same year with temperatures sufficient for development to occur, that is exactly what happens, so long as temperatures allow for development.

This past spring I was surprised to see a male Hyalophora columbia Columbia flying around in my living room in very late May. It was much too cold out to be a wild male that somehow flew inside. We still had considerable snow on the ground at that time in shaded places. I assume that one of the larvae which had not pupated in a torn cocoon that I had harvested, escaped from a storage tub on the kitchen table and finished spinning under the table or again under baseboard radiation cover. For sure the cocoon/pupa never experienced any freezing temperature that winter. The coolest my house ever gets in the winter time is upper 50's F.

You will find it written in highly regarded texts that Columbia need to experience a hard freeze followed by warming in order to be able to break diapause.. When I first started rearing Columbia, I would keep the cocoons in sealed plastic tubs in fridge crisper in the fall and early winter and then put them outside for a week or so to make sure they experienced a hard freeze. Now I just keep my overwintering columbia cocoons, October to early May in sealed plastic tubs in the refrigerator crisper from late October until early May and I always get 100% eclosions of nice specimens that have never experienced a hard freeze. Crisper temperature never dropped below 38F. reproduction follows successfully.

Many many years ago I reared Saturnia pyri on pin cherry and I always found them to be single brooded. In some European countries they begin flying in very early spring while in other countries it seems they begin flight into late spring, always as a single brood. I am pretty sure that both times I reared them that I had at least one cocoon that spent two years in diapause even though all cocoons were stored in fridge in plastic tubs from October until May and all stock came from same parentage.

I think many of the single brooded species work diapause on some sort of internal clock, but there are probably temperature factors, photo period factors and possibly slight genetic differences that result in even siblings doing different things regarding diapause even under identical conditions.

You will just have to wait and see what happens. You might get a partial second brood, but I think that is much less likely than all pupae will overwinter, and you might even find that the odd one will spend a second winter in diapause. Please let us know what happens.

I also have first hand experience with H. columbia gloveri (western columbia) and H. euryalus and even Citheronia regalis spending more than one winter in diapause, and I have heard from very reliable sources that some African species spend multiple years in diapause especially during years of drought.

Bill Oehlke

PS My father once reported to me that some polyphemus cocoons he had sold to a zoo were left accidentally in cold storage from October of one year until spring TWO years later. The cocoons yielded healthy moths. That is not first hand experience, but I think one of these years when I have an abundance of cocoons I will intentionally keep some cocoons in cold storage for two consecutive inters without a warming period just to see what happens. I do not know at what temperature the zoo was storing the cocoons.

It is easy to sex pupae of Lepidoptera with a hand lens. Here is how to tell the difference:



Also if you examine the antennae on the pupa the male antennae will be broader than those of the female in Saturniidae. In some species this can be less obvious than in most, but in many species the difference is really obvious.

Adam.