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Insect Quiz September, 2006 |
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Insect Quiz September, 2006 |
You have noticed small green ‘bugs’ in your garden during August and September. They have been found eating the petals of a variety of flowers, including roses and dahlias. You did not see these insects earlier this summer.
1. What is this insect?
This is a northern corn rootworm, Diabrotica barberi. This insect is small, about 3/16th inch long, and is a pale, uniform green, lacking any markings (i.e. spots or stripes). It is common in the Midwest and Minnesota wherever corn is grown. In Minnesota, that is generally in the south and western areas of the state.
2. What is its life cycle?
This beetle typically has a one year life cycle, although it is possible that it can be extended to two years. Northern corn rootworms overwinter as eggs which are laid in the soil at the base of corn plants. They hatch the following June and the larvae start to feed on corn roots. The larvae are active for four to six weeks before pupating. They emerge as adults in July, about five to ten days after they pupate. After feeding they lay eggs, generally during August and September.
3. What kind of damage does it cause?
As larvae they are very damaging to corn plants by feeding on the roots. However larvae are not found in gardens (except on corn). Adults typically feed on corn silk and pollen although they don’t cause any damage to corn plants. As the corn dries, the beetles will fly off in search of food which often takes them to gardens. Here, they will feed on the blossoms of flowers, especially light colored ones, chewing ragged holes and making blossoms unsightly. The level of this damage can range from slight to severe.
4. What is the best management of this insect?
You have several options if you have a problem with northern corn rootworms in your garden. You can ignore them especially if they are not very abundant. You could also physically remove them by shaking plants so the beetles fall into a pail of soapy water. You could also erect a barrier around the plants, like a floating row cover to protect a limited number of flowers. If they are numerous, you may need to resort to an insecticide to protect your plants. Common examples include permethrin, esfenvalerate, or bifenthrin. Be careful spraying your garden as insecticides may kill bees that pollinate flowers.
