At our recent garden club meeting, we discussed the voracious Catawba worm that feeds on Catalpa trees and other in the same family. We did not know much about them but with a little more research I realized that I had actually seen them before as a moth. They are the ones that fly like a hummingbird and feed on flowers in much the same fashion. The worm has a little spike, much like the tomato horned worm.
One of our members was having a particular fir with them, so we researched and found out that in some areas they actually have a festival named after them! A festival for a caterpillar that can eat a tree clean of its' leaves? How could that be?
It seems that they are a favorite fishing bait, so much so that there are actually Catawba worm farms! Yikes! A number of articles suggest fisherman as a natural control. Amazing!
After I got over the uniqueness of this problem I got more serious finding a control.. Sure enough, hand picking is an option for small trees, so is using Sevin but I would caution you from spraying something up in the air without a very good breathing mask. A leak of methyl isocyanate from a Union Carbide plant making Sevin in Bhopal, India killed at a minimum 3,800 people back in 1984 soÖ.. be careful.
Other solutions would be to encourage or release a beneficial wasp that plants eggs in the caterpillars and quickly parasitizes the worm. The trichogamma is one such wasp that can be bought from commercial breeders and it the one responsible for the tiny white cocoons we see attached to the tomato horned worm. From experience with tomatoes, too many caterpillars survive, so I would consider some additional options.
Apparently, the first generation of the year is not deadly to the catalpa tree. It grows another batch of leaves and moves on, BUT the Catawba worm can have several generations in a year and if they continue to attack, they can eventually weaken the tree. Another such attack the second year could finish the weakened tree off.
Learning the whole cycle of the worm provides more options to try to reduce and eliminate the popular and notorious insect. They over-winter in the ground, so there might be a soil nematode (also raised by insectaries) that could be applied to the ground, much like the Japanese Beetle. Also, the worms apparently crawl back down to burrow in the soil around the base of the tree after they have eaten their fill so their trek back down could be intercepted by wrapping a tree wrap around the trunk and then applying a sticky product like Tanglefoot http://www.tanglefoot.com/products/barrier.htm. You can probably make your own home-made product with a little thought.