Q: There are small insects about 2-3 millimeters long that are eating (and killing) our Mexican pink flowered Oenothera.Β I put a pan underneath the damaged leaves and knocked about five off. They have killed about three-quarters of my plants, mostly those in the sun. Part is behind a wall that only has eastern light in the early morning and also is under the place in the eaves where the water rushes off the roof and so far they look healthy, so I will be able to replant.
A:Β The insects in the photo are larvae of the apple flea beetle (Altica foliaceae). They are common across the United States. In the west they are commonly found on evening primrose. When populations of these beetles are high, as they often are in the late summer and into fall in southern Arizona, they can do a lot of chewing damage. While there are some insecticides available for managing leaf beetles, these insects can also be ignored this late in the growing season. Since the Mexican evening primrose is a tough plant that will grow back from the roots, you can simply cut it back to the stem. This also serves to reduce places for the beetles to spend the winter. If you desire to spray them regardless, the least toxic chemicals include insecticidal soap with pyrethrin and neem products.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed toΒ plwarren@cals.arizona.edu
