A serious and deadly viral disease of caterpillars, NPV is likely the most dreaded disease among butterfly farmers. Once a few larvae become infected with this virus, the contents of every infected cage must be destroyed and the entire room and everything in it completely sanitized.
Signs and symptoms of NPV often include many of these:
- A loss of appetite which results in smaller caterpillars and smaller pupae
- The caterpillars are sluggish or don’t move at all
- Frass is liquid instead of solid
- Caterpillars look deflated
- The caterpillar’s skin (cuticle) appears to be darker than normal and easily ruptures
- Caterpillar’s yellow, black, and white stripes appear dirty-looking
- Caterpillars and pupae literally appear to melt, spilling a foul smelling liquid
- A peculiar, foul odor is present in the room where the caterpillars are housed
- Infected larvae climb to a high point in the cage and die, either hanging straight down and appearing elongated, or hanging in an inverted “V” (attached by their middle prolegs
- Monarch pupae infected with this virus turn from light green to yellowish and then brownish-black.
- Pupae often rupture when touched, releasing a foul smelling liquid
The foul smelling liquid which is released by infected larvae and pupae contains pathogens which can become airborne and then settle on counter tops, walls, onto foliage that will be consumed by other caterpillars, and on to the clothing of people who are working in the contaminated area. Until every contaminated item is destroyed or sanitized, there remains a risk of spreading this deadly virus to healthy caterpillars.
Should any potentially infected adults survive from an NPV-infected batch of larvae, those adults should be destroyed. Never should they be considered for use as breeding stock and never should they be released into the wild. NPV can be inside the eggs laid by NPV-infected adults and there is no way to sanitize the contents of eggs.
Once potentially infected equipment is sanitized and rinsed, it might be wise to allow it to sit in direct sunlight for six hours or more. Sunlight is believed to kill NPV. Don’t rely on the sun to do the job of killing the pathogens though. Always sanitize the equipment and then sit it in the sun