Q: Tiny black insects are making lace out of the leaves of my Yellow Bells. I spray with Sevin twice a day but it has had no effect.
A:Β The tiny black insects are actually the frass (aka poop) from tiny caterpillars. These caterpillars are sometimes called the Tecoma leaf tiers or sesame leaf tiers (Antigastra catalaunalis) due to the way they wrap themselves in leaves with their silk when ready to pupate. Before that happens they chew on the top leaves, the new growth, of Tecoma stans (yellow bells). Sevin should work on these caterpillars although applying it twice a day seems like way too much. Please check the label to see how often they recommend spraying. I am surprised it isnβt working. You might be spraying at a time when they arenβt active or in the line of fire. Sevin is a nerve poison that works when contacted or eaten so the caterpillars need to be present at the time you spray or soon after.
The unfortunate thing about Sevin is that it is toxic to beneficial insects including honeybees. Another insecticide you can use instead is Bt (Bacillus thuringiensis). This insecticide, sometimes sold as Dipel, can be sprayed on the leaves in the area where they are feeding.
The nice thing about Bt is it wonβt harm other insects that might help you by eating the caterpillars.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
