Brimstone larva hanging in a J

[chrisox]

I have been rearing some Brimstone caterpillars I found from freshly laid eggs. Two have now pupated fine, but one hung in a J position from a leave with no silk thread around it's body. A couple of days later I found it had gone a nasty dark green and had died. I can't tell if it died whilst trying to pupate. I can post a picture of it dead but it's not very pleasant. Anyone seen anything like this before?

Cheers

Chris

[Vince Massimo]

Hi Chris, these things happen, particularly at critical points in the development of the larva or pupa when internal changes are taking place. These include leading up to moulting, pupation and adult emergence. I have lost numerous larvae of different species at such points, so it should not be a cause for undue concern, as I doubt there is anything you could have done about it.

Vince

[KeithS]

Did any of your buckthorn leaves have a whitish fungus on the back? I’ve found that to be associated with the symptoms you describe. From my own experience, larger brimstone larvae also do not appreciate crowding nor heat/direct sun.

[chrisox]

I don't believe the buckthorn leaves had any fungus. I tried to choose the healthiest looking leaves and replaced the foodplant with fresh every few days and regularly cleaned out the frass. I had five large larvae on two buckthorn branches each about 1½ foot tall in a cage, I don't know if that counts as crowded. I did loose another early instar one after it had moulted; it seemed it just decided to die. I kept them in my north facing bedroom near the window, so not direct sunlight, although it might have got a bit stuffy in there. All the remaining four seem to be ok and have either pupated or are correctly hanging ready to pupate. I found it strange that the larva didn't set it self up with a silk thread round it's middle but hung in a J rather like a small tort.

Thanks for the responses. I accept these things happen.

Cheers

Chris

[Vince Massimo]

Keith makes a good point. I forgot to mention that fungal, viral and bacterial diseases also take their toll on larvae. The fact that it went a nasty colour soon after dying could suggest that there was a pathological cause for the death. It must have died mid-way through spinning-up, before adding the final strands of silk which supported its body, which would explain its unusual position at the end. I did have a larva in 2011 which spun-up in the normal way, but then slipped out of its supporting girdle during the contortions of pupation. It ended up suspended by its tail, but the butterfly emerged without any problems.

Brimstone pupa 25-June-2011

Vince

[KeithS]

I don't believe the buckthorn leaves had any fungus. I tried to choose the healthiest looking leaves and replaced the foodplant with fresh every few days and regularly cleaned out the frass. I had five large larvae on two buckthorn branches each about 1½ foot tall in a cage, I don't know if that counts as crowded. I did loose another early instar one after it had moulted; it seemed it just decided to die. I kept them in my north facing bedroom near the window, so not direct sunlight, although it might have got a bit stuffy in there. All the remaining four seem to be ok and have either pupated or are correctly hanging ready to pupate. I found it strange that the larva didn't set it self up with a silk thread round it's middle but hung in a J rather like a small tort.

Thanks for the responses. I accept these things happen.

Cheers

Chris

Doesn’t sound like you are doing too much wrong. I keep mine on growing netted foodplant outdoors: I have a few small Buckthorn bushes in pots so things are as “natural” as possible, but I still occasionally lose a few larvae in the same manner you describe. Early season larvae from eggs laid up to mid May generally seem to be ok, but the mortality rate seems to go up, the later the season. I’ve associated this with heat, and also with that leaf fungus that seems to occur from June onwards, but neither may have anything to do with it. If the foodplant is fresh, conditions clean, dry and well-ventilated, and the larvae are not overcrowded, then you really can do no more! I have also found Brimstones to be a bit fussy if that’s any consolation.

Oh, and watch out for spiders and earwigs as well. Even small ones seem to like biting larvae that cannot move quickly enough to brush them off and that also makes for a few pre-pupal victims, though that’s true for any caterpillar of course!

[chrisox]

I know this topic is a bit old now, but of the 13 Brimstone eggs I found on my Alder Buckthorn I'm pleased that nine seem to have survived into healthy large caterpillars. However I have noticed a whiteness on the top of some of the leaves they are eating. Could this be the white fungus you were talking about KeithS?

Cheers

Chris

[bugboy]

The white actually looks like silk spun by the caterpillar on which it moults on. It grips the silk with its old feet and uses it as an anchor point to crawl out in its new skin

[PhilBJohnson]

I was happier with this mobile phone image, than some previously taken.
For iPhone quick focus on something small, one zoomed in to subject, by using thumb and index finger on screen, slowly moving them apart. This was also thought to move the pixels further apart, reducing file size (so one didn’t zoom in too far).
Then one refocused by a tap on the screen with one finger, on the specific subject position (Where the small yellow box appeared).

June 17th 2020, Lincolnshire 5th Instar Resting Position

Brimstone Larva
It was thought that eggs laid early in April, developed faster and might have entered pupation first (or were predated first). Very small larva, hatched from eggs laid later in the year, might have avoided first predation and then left alone in smaller numbers to survive.
Kind Regards

[chrisox]

The white actually looks like silk spun by the caterpillar on which it moults on. It grips the silk with its old feet and uses it as an anchor point to crawl out in its new skin

Interesting, yes I guess caterpillars need something to hold their old skin/feet firm while they crawl out of it. There is no old skin left to see here of course as Brimstones eat their old skins. Looking at the Buckthorn bush these white patches are all in the centre upper side of leaves where the caterpillars would be when moulting. You learn something every day

Cheers

Chris