Three species of beetles are making pests of themselves in my garden this year. First is the larvae of the Colorado potato beetle, which concentrate on the eggplant leaves.
As you can see, they have been chewing on the edges of the leaves. I caught several of them a few days ago, and found fifteen more this morning. I picked them off the leaves and dropped them into a container of soapy water to drown. I didn’t take any photos of the larvae before I disposed of them, but you can see photos and more information in this post I wrote last year.
Another beetle attacks my eggplant every year. Flea beetles chew dozens of small holes in the eggplant leaves. If there are enough beetles, they can make the leaves look like lace.
I haven’t found a good means to control flea beetles. They are too small and quick for me to catch them. I tried insecticide several years ago. It seemed to work the first time but not the next year, although I doubt they built up immunity that quickly. I’ve also tried spraying water on the leaves to knock them off, and that might help for a little while.
The third beetle pest is the Japanese beetle (Popillia japonica). There are more of them than I remember seeing last year, but not as many as we had several years ago. They seem to attack a different plant each year. Last year, I had them on my marigolds and beans. This year, they are concentrating on the “volunteer” morning glory vines.
Colorful little rascals, aren’t they? I’ve tried three methods to get rid of them. I treated my lawn with milky spore (Bacillus popilliae Dutky and/or B. lentimorbus Dutky) several years ago. These bacteria attack the beetle grubs while they are growing in the soil. The problems with that method are that you need some Japanese beetle grubs to spread the bacteria throughout the soil, and if your neighbors don’t treat their lawns, then their grubs will attack your plants after they metamorphose into adults.
I’ve also used Japanese beetle traps in the past. These use flower scent and beetle pheromones to lure the beetles into the traps. I placed them upwind of my flowers and vegetables, but they may have attracted more beetles than they killed.
The method I use now, at least when there aren’t too many beetles, is to knock them off the leaves into a container of soapy water to drown, much like I do with the Colorado potato beetle larvae. If you try to catch the Japanese beetles, they can escape either by flying away or by dropping to the ground.
When the first beetles emerge, they find a tasty leaf and start eating. They release pheromones that attract other beetles. This is why they attack different plants in my backyard every year. They seem to like plants with large leaves, perhaps because they are easy to sit on and they provide a lot of food. I’ve had them attack cherry leaves, rose flowers, bean leaves, basil leaves, fern fronds, and now morning glory leaves.
As to why they all congregate in one place, take a look at the next photo.
Sadly for these two lovers, they ended up in my container of soapy water.