To me this is pretty fascinating. I don’t know if it’s true in all cases, but many arthropod larvae completely liquefy inside the pupa, their bodies completely disassembling and reconstituting itself as a butterfly (or whatever). Now, what if I kept a caterpillar, for example, form pupating? Would it just die? Would it fall apart? The onychophorans live their whole lives as eruciform critters (OK, I know they’re not closely related), and they’ve done quite well for a long time.
Similarly, barnacles, before they anchor and start building their home, look much more crustacean-like than their adult brethren. If I kept one from anchoring, would it just starve to death?
(Not that I would actually try to do this with either one.)
Flies, the holometabolous insect with which I am familiar, can’t be stopped from pupating. It is dependent on a number of factors which lead to an ecdysone pulse. As wandering third instar larvae, they will just eventually crawl and stick on something and pupate when they get that pulse. Their cuticles harden and over the next two days, their imaginal discs evert as form a new body. There are some Drosophila mutants in this process – those larvae just grow, wander, and then die. To me, your question is akin to asking “What would happen if I prevented a mammal from entering puberty?” You can’t prevent it, and if you could, nothing would happen.
But a mammal’s puberty isn’t dependent on its performing particular actions. Even a quadriplegic child will still enter puberty. The OP is referring to animals that pupate by going through specific actions, and it’s possible to prevent those actions.
I disagree, at least partly; it actually looks like the OP is under the impression that the insect pupa is something that the larva builds around itself, rather than something the larva becomes, which is pretty much the case.
Yes, it would be unable to feed and would eventually starve to death. This is like asking what would happen if you prevented hibernating animal form waking up. Of course it would eventually die, It has been confined to a location and state where it simply cannot obtain food.
Eventually, yes. Once again, the case material is only intended for short term use. In arthropods that ;live extended lives they always moult at least once a year to allow for growth and to repair damage to their casing. You have prevented that from happening, the animal has to fall apart eventually simply because it is unable to repair it’s own exoskeleton.
That depends entirely on how you intend to prevent metamorphosis. Barnacles go through three distinct stages. The first is a free living feeding stage, the second is the wandering stage that lacks a mouth and exists only to find a suitable attachment point. Naturally if you stall development at that point the animal will die, it has no mouth. If you stall development at the earlier naupliar stage then there is no good reason why it should starve to death.
Once again though, you haven’t allowed any mechanism for future moulting, so eventually the animal must die simply because it has outgrown its own skin, or because it can’t repair damage and wear.
Blake, I thought he was asking not about how you could keep a butterfly from hatching - of course it would die. But could you keep a caterpillar from making it’s little casing thing in the first place? Could you somehow force it to remain as a caterpillar all of its life? Aren’t there some types of caterpillars that have to hang on a branch to start pupating or… something along those lines?
Oh, sorry. I got confused when you said that it would be unable to eat. Why would it not be able to just keep eating and growing as a caterpillar? Is there some kind of chemical transformation in it’s body that forces it not to remain a caterpillar? On one hand it seems like a stupid question akin to, “why can’t a fetus just stay inside its mother eating and growing forever?” but on the other hand… I’m still not getting it.
I would think that you could prevent it. You may need to remove a gland here and there, take out the gonads, administer certain hormones, administer hormone blockers, and possibly control the diet, but I would think you could do it. OTTOMH The diet and exercise regimen of female gymnasts often delays menarche by several years.
Samm
I think part of the problem is that some of the posters are using terms in a precise scientific manner. It would help the rest of us if one of them could give a description of the lifecycle of a representative insect, explaining the terms. At present we seem to have
“Could I stop the butterfly from pupating?” (meaning could I prevent a caterpillar from entering the next development stage and building a cocoon)
“No, once the animal has entered the chrysalis, pupation is automatic. Preventing it would result in the organism starving to death inside the chrysalis”
BTW
Gould did an essay on a species of fly that changes reproductive and developmental cycles depending on how much food is available. Abundant food results in females parthogenically producing more females who remain larvae throughout their lives and parthogenically produce daughters who do the same.
In order to carry on eating and growing as a caterpillar, it would have to shed its skin and, as I understand it, this eventually results in it shedding its skin to reveal the pupal body underneath. I’m not sure to what extent the controlling factors of this are genetic, hormonal, dietary, body-mass and generally environmental, but in order to keep it growing as a larva, you’d have to permit the changes that allow it to shed its skin, but attenuate those that result in the formation of the pupa.
It may be that the systems with which you’d have to interfere are so intertwined and cross-related, that you can’t just turn one part of it off without affecting something else; something vital; genetics especially is often like that.
Larval maturation and pupation is controlled by the amount of “Juvenile Hormone” secreted by the Corpora Allata gland at the base of the brain. This gland can be removed from a young larva and implanted into a 5th instar larva, the extra hormone produced will force the larva (caterpillar) to molt into a larger 6th instar rather than pupate. These experiments were originally done by Dr Wigglesworth (what a name!). I repeated them in college and produced 6th and 7th instar Anise Swallowtail larvae. Very large, they continued eating, but died rather than ever reaching a pupal stage.
I wonder what would happen if, rather than implanting the gland, you merely dosed the larva with the hormone until it was very large, then stopped and allowed it to pupate; or would it simply not be able to do so, having run out of ‘stages’, as it were.
OK. Thanks. I was thinking about the larva “creating” a pupal case (like a cocoon), but I see that’s not the case. Instead the outer “skin” becomes the pupal case.
I may be able to answer that question later this year. I raise Saturniid moths (example of one type) and have been toying with the idea of using commercially available Juvenile Hormone to play with growth and molting. Since it is now available from chemical suppliers, there is no need to slice-and-dice out the gland and bother with transplantation. Stay tuned…
So what if you prevent a caterpillar which builds a cocoon from doing so? Will it still become a pupa absent a cocoon and eventually an adult, or will it die trying to build one or what?
Thanks for that link, lots of clarifying info there. And well, of course if your name were Wigglesworth, you’d just have to be an entomologist. Quite the trickster, too, loved the photo where he traced his initials on the insect with JH !
I do wonder, though, how do you perform brain surgery on a caterpillar??? Love to hear details, TwoTrouts. I see in your last post that you no longer need to do that due to the hormone being commercially available, but, still am curious about the process.
