If a bug has turned your garden into its personal salad bar, you may wonder what kind of creature to blame. Examining the type of damage the bug caused provides a strong clue as to which pest visited your yard. If portions of leaves look as if they were cut away, then the culprit may be a kind of bee, weevil, beetle or caterpillar.
If circular portions are missing from edges of leaves, then the leaf-cutter bee (Megachile rotundata) may be to blame. You may even see the 1/4-inch-long, grayish bee at work on a leaf. A leaf-cutter bee removes pieces of leaves and uses the pieces to line its nest. The bee rarely causes long-term damage to a plant. Because leaf-cutter bee is a beneficial pollinator, you shouldn't wage war against it. Instead, cover affected plants with cheesecloth to prevent further damage.
Black Vine Weevil
Weevils are closely related to beetles and one kind, the black vine weevil (Otiorhynchus sulcatus), makes a meal out of leaves. The weevil cuts notches into the edges of leaves and creates tunnel-like holes from the edges inward. The damage won't kill a plant, but the weevil's larvae can wreak havoc on the plant's roots. Control adult black vine weevils by picking the 1/2-inch-long, black bugs off your plants. Control their larvae by applying beneficial nematodes to soil in spring. Other kinds of weevils chew holes randomly throughout leaves.
Flea beetle is the common name applied to many species that chew small holes in various places across plant leaves. The beetles are named "flea beetle" because of their tiny size and habit of jumping like a flea. Although each species chooses a few plants as its favorite meal, often vegetable plants are affected. Although mature plants can handle most flea beetle damage, seedlings can be killed by a hungry batch. Because flea beetles are most active in early spring, you can prevent some of their damage by planting your vegetable seedlings as late in the season as possible. Placing sticky traps under the plants helps to control a flea beetle infestation because the insects stick to those traps.
Although caterpillars are entertaining to watch and many turn into butterflies or moths, the critters can cause serious damage to a garden. Caterpillars such as hornworms (Manduca sp.) and cabbage loopers (Trichoplusia ni) chew large, irregular holes in leaf edges and cut holes in the center of leaves. Control caterpillars by picking them off your plants. Because birds and beneficial insects gobble up caterpillars, encourage those hunters to visit your yard. Certain viruses and parasites target caterpillars but should be used only when caterpillar infestations are heavy.
- The New Sunset Western Garden Book; Kathleen Norris Brenzel, Editor
- Arizona Master Gardener Manual: Symptoms and Signs of Insects, Mites and Other Animals
- Missouri Botanical Garden: Beetles -- Surface Feeders
- Missouri Botanical Garden: Flea Beetle
- University of California Integrated Pest Management Online: Leaf-Feeding Caterpillars on Flowers and Vegetables
- University of California Integrated Pest Management Online: Black Vine Weevil -- Otiorhynchus Sulcatus
- Missouri Botanical Garden: Leaf-Cutter Bees
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