MASSIVE mortality of Agraulis vanillae larvae is vexing me

Hey Leroy,

Google "NPV virus production" and you'll hit a gold mine. Basically you raise a bunch of larvae that look like Clark's, and in the old days, you just ground them up and sprayed them (and hope that your sprayer didn't plug up).

it's really that simple - but hard to mass produce.

John

I am taking this to the "Porch Light"

Clark, have you tried Oxine. I've had great success with that stuff.

I am also in Southern California.
I haven't found any dead fritillary caterpillars, just haven't seen any big ones. That could have something to do with the fluctuating weather. If this is an NPV infection, I actually don't think that cutting down the vines will necessarily solve the problem permanently. It seems that this virus is ON the plants, not IN the plants, so treating it like a plant virus (destroying affected plants) may make the situation worse for the surviving butterflies. I have a pretty good knowledge of pathology (I have weird interests sometimes) and this seems to behave like a topically transmitted infection, i.e. infected body fluid transmits the disease to other individuals that come in direct contact with the contaminated fluid.

Unfortunately, as with any other insect disease, I doubt there is any information on how long it can survive outside of a host, so isolating the plants for a decontamination period would be a crap shoot at best. Someone suggested vinegar - a pretty well known defoliant - in small quantities to remove the virus since it is acid based. While this may work, you may also end up destroying your plants. Although it can also be a defoliant, I've been able to use 70% isopropyl alcohol in a bottle with a fine mist sprayer in the past to treat certain plants. This is a known anti viral, and can act as either a base or acid, depending on the circumstances, if I remember correctly. It does not kill ALL viruses, but something like 99% of them, so the odds are good. I've never tried it on passionvine, but it may be worth a shot. It evaporates quickly, but leaves nearly no residue. The downside is that it will kill EVERYTHING insect on the plants if it comes in direct contact with them - eggs, caterpillars, spiders, etc.

If the virus thrives in an alkaline environment, any soaps, anti-fungals, etc. that are applied to them may contribute to the spread of the contaminant when water hits it, so these should be discontinued while trying to eliminate the virus. Since the transmission method appears to be direct contact, it may also be a good idea to collect any dead caterpillars, frass, dropped leaves, or fluid stains from the carcasses and burn them. No virus likes fire.

UV light is another pretty good way to wipe out most viruses. I don't think they are particularly cheap, but portable UV sterilization lights are available. You could potentially use one of these (maybe run it over the plants a twice a day for a few minutes each time?) to remove any remaining surface virus. Effects on the plant itself or uninfected eggs and caterpillars are unknown. I've never tried this. If you have many large plants, though, this may not be viable.

A potted plant could be isolated, disinfected with alcohol and/or UV, then have non-infected individuals (or adult butterflies) re-introduced to it to see if this method has an effect on the transmission of the virus.

Hope this helps.

I had the same kind of thing happen a few years ago when rearing painted ladies. I lost a couple hundred. I thought it was because of too much moisture in my enclosure because most of the air holes had become plugged and I didn't notice. Since I was using artificial food, I never had to open the tank and it got quite humid in there. Perhaps it was a virus. Maybe the recent late-season rain and low temps help the virus propagate?

I'm going to try sterilizing a few of my plants and see if that helps at all. I still see adult butterflies come through my yard from time to time...