Walliser: Some beetles are real pests
There are more than 350,000 species of beetles in the world. All have two pairs of wings. The outer wings create a shell-like covering over the membranous wings used for flight. Beetles go through complete metamorphosis, passing through life first as an egg, then a larvae, a pupae and finally an adult.
Some beetle species are decomposers, feeding on animal and plant wastes, while others feed on fungus, pollen or nectar. There are also predatory beetles, such as ground beetles, ladybugs and tiger beetles, that consume other insects.
Most beetles are harmless to people and plants. But there are a handful of beetle species that can become problematic in gardens. Here are five of the most common pest beetle species in Western Pennsylvania.
Cucumber beetles: Both common species of cucumber beetle, striped and spotted, measure one-quarter inch long. Adults are yellowish green. Striped species have three broad black stripes while spotted species have black spots. All species feed on members of the cucurbit family, including cucumbers, melons, pumpkins and squash. They chew ragged holes in flowers and foliage, and spread bacterial wilt and cucumber mosaic virus.
Colorado potato beetles: Both the tan and black striped adult beetles and their chubby, rose-colored larvae feed on the foliage of potatoes. Severe infestations can be devastating as the beetles can quickly defoliate entire plants. Colorado potato beetles are famed for their ability to gain rapid resistance to chemical pesticides, making them difficult to control. They can go from egg to adult in a mere 21 days.
Asparagus beetles: Though this beetle has only one host, asparagus, it can cause significant damage. Adults chew depressions in developing spears, and the army-green larvae chew the maturing ferns, limiting photosynthesis and decreasing yields. Adult asparagus beetles are one-quarter inch long. They're black with several cream-colored spots and red wing borders.
Mexican bean beetles: Adult Mexican bean beetles look a lot like ladybugs on steroids, though the absence of white markings between the head and body easily distinguishes them from ladybugs. Their copper-colored wings have 16 black spots. The larvae are light yellow and covered in bristly spines. Bean beetles skeletonize bean leaves and are often found on the leaf undersides.
Japanese beetles: Introduced to North America from Asia, Japanese beetles have become a notorious pest. Adults are metallic green with copper-colored wing covers. Their ground-dwelling larvae are C-shaped, grayish-white grubs with light brown heads. The grubs feed on the roots of turf grass while adult beetles eat a broad range of plant material.
To mitigate damage from these members of the beetle family, include lots of flowering plants in and around your vegetable garden to encourage the predatory insects who feed on the beetles.
Cover susceptible crops with a layer of floating row cover or tulle fabric to keep the pests from accessing the plants, and hand-squish any larvae and adults that become problematic.
As a last resort, in the case of severe infestations that cannot be handled by row covers and hand-removal, spinosad-based pesticides are effective against a broad range of beetle species. These products should never be used when bees and other pollinators are around, so be careful to spray only in the morning or evening, when these beneficial insects are not active. Follow all label instructions.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden: A Natural Approach to Pest Control” and “Good Bug, Bad Bug.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
