MISSOURI — This year from the Arkansas border to the Iowa border, gardeners in Missouri are dealing with beetles, whether it be cucumber beetles, potato beetles, bean leaf beetles, or Blister and Japanese beetles.
Blister Beetles are members of a family of plant-feeding insects (Meloidae) that contain cantharidin, a toxic defensive chemical that protects them from predators. Accidentally crushing a beetle against the skin can result in a painful blister, the source of the insect’s common name. Animals may be poisoned by eating crushed beetles in cured hay. The severity of the reaction, ranging from temporary poisoning, to reduced digestive ability, to death, depends upon the amount of cantharidin ingested and the size and health of the animal.
Adult blister beetles are often seen visiting flowers for food and mating opportunities. Several blister beetles prefer flowers in the sunflower family, which abound in prairies, old fields, pastures, along roadsides and other sunny places. But at least one species, for example, focuses on flowers of apple, plum and other rose family trees. Others spend more time on the ground laying eggs in the soil. Adults visit flowers to eat, nectar, pollen and sometimes entire flowers. Some species eat leaves. Different types of blister beetles prefer different plant families; most prevalent are plants in the sunflower, bean and potato families.
The larvae of most blister beetles are parasitic on ground-nesting, solitary bees, eating the pollen, nectar and honey stored for the bees’s young, plus the eggs and young themselves. The larvae of some groups eat the egg clusters of grasshoppers. Blister beetle numbers increase dramatically following a dry summer with high grasshopper numbers.
Four species of blister beetles are relatively common in the Midwest. They include the ash gray, striped, margined and black. They have narrow, elongated, cylindrical bodies, and are ½-3/4 inch long. There are no known predators or parasites that effectively control blister beetles. If you choose to spray for them, the following are recommended: Permethrin (Bonide Eight and Hi-Yield Lawn, Garden and Farm Insect Control) and Cyfluthrin (BioAdvanced Vegetable and Garden Insect Spray). Always follow label directions.
Japanese beetles are 3/8″ (8-11 mm) long and ¼” (5-7 mm) wide, brilliant metallic green insects with copper-brown wings whose hard body makes them unpalatable to many predators, including birds. The larvae, called grubs, are grayish-white with a dark brown head. They are C-shaped when disturbed. They are found in the soil where they feed on the tender roots of vegetables, lawn grasses, and other plants. Japanese beetles overwinter as a partially grown grub in the soil below the frost line. The grubs resume feeding on grass roots in the spring, and then pupate near the soil surface. Adults emerge between May and July, depending on their geographic location.
Avoid planting the most susceptible plants: roses, grapes, and rose of Sharon; apple and crabapple, mountain ash, grey birch, American and horse chestnut, elm, linden, Japanese and Norway maple, London plane tree, Lombardy poplar, Prunus (cherry, etc.), sassafras, and black walnut.
To control adults, pyrethrum or Neem, can be applied in two applications, 3 to 4 days apart, to control the problem. If something stronger is needed, carbaryl
(Sevin) may be used (every 5-10 days during heavy infestation). Do not use pheromone traps. Research has found that pheromone traps attract many more beetles than they catch and probably do more harm than good to plants in the beetles’ flight path and near the traps. Their use is not recommended.