I have been finding leaves of some of my plants with holes in them and some shredded with only veins left. One surprising plant being eaten is the leaves of my rhubarb. I do notice the damage is being done during the night. This clue tells me the insect doing the chewing is a nocturnal one. A little scouting with a flash light in the dark reveals the Asiatic Garden Beetle( Maladera castanea) voraciously munching away! During the day they hide in the mulch and soil just below the plants. Carefully pull the mulch away and scrape small amounts of soil to reveal the beetles sleeping quarters during the daytime. I hand squish the ones I can find during the day or drop them into a jar of soapy water. I am finding about 20 per plant every few days. They must be flying in during the night from other areas. Other plants they seem to feed heavily on are basil and peppers. Tomatoes are not being damaged at all. The pink petals of my coneflowers are completely missing thanks to these beetles’ nocturnal foraging.
Asiatic Garden Beetles are reddish-brown beetles a little smaller than the Japanese beetles. I like to call them cinnamon colored so people don’t confuse them with the bright red lily leaf beetle. All beetles have complete metamorphosis, four very different stages of life. They start off as an egg, hatch into a white grub typically found in lawns, then pupate under ground, then change into the adult beetle.
Here in CT there is one generation per year. The adult beetles emerge from the soil July through August. They feed on above ground plant parts, mate, and the female lays eggs in the soil. The eggs hatch into grubs during the next few weeks and feed on plant roots until the cold weather triggers them to move deeper into the soil. The grubs overwinter until the spring warms the soil at which time the grubs move up the begin feeding on the plant roots once again. Around June the grubs will pupate to become adult beetles rising out of the soil in July and cycle begins again.
Control measures are handpicking from the soil during the day or from the plants at night. Row covers of remay will exclude the beetles from landing on the plants but will need to be removed if your plants need to be pollinated to let in the bees.
The grub stage is easiest to kill by applying grub control to lawns. Merit (Imidacloprid) is a commonly used in grub killer formulations. If you kill these grubs, they will not grow up to be next year’s beetles.
To kill the adults presently eating the garden, chemical controls recommended are pyrethrin, rotenone or Sevin (Carbaryl).