Eric Rebek, Oklahoma State University, and Eric Stafne, Mississippi State University
Adult wheel bug (Arilus cristatus). Photo by Becky Hunn, On the Edge Vineyard.
Adult assassin bug (Zelus sp.). Photo by Louis Tedders, USDA Agricultural Research Service, Bugwood.org.
Assassin bugs are important predators, since both adults and nymphs feed on a variety of insect pests. Some species specialize on one particular prey type such as ants, while others are generalists, feeding on anything from small items such as aphids and insect eggs to larger prey such as leafhoppers and caterpillars. They may even feed on other benficial insect species. Even though assassin bugs are mostly predaceous, they should be handled with care or just left alone when found because they can inflict a painful bite.
Assassin bugs are quite mobile and are found in a variety of habitats, but they will most often be found in vegetation, searching for prey. The adults are poor flyers, but adults and nymphs will move rapidly if disturbed. Several species of assassin bugs can be encountered in the vineyard. One of the most commonly encountered species in the southern Great Plains is the wheel bug (Arilus cristatus). The wheel bug is distinctive because it has a crest behind its head that resembles a cog wheel. Other species include the spined assassin bug (Sinea diadema and Zelus species).
Assassin bugs vary widely in size and color. Adults can be as long as 1½ inches and range from brown or gray to bright orange with stripes. Assassin bugs have large, grasping front legs, narrow heads, and a long, three-segmented “beak”. The abdomen also extends past the wings in the adults. Assassin bugs undergo gradual metamorphosis, and the nymphs resemble adults, except they lack fully formed wings. Eggs are brown and laid in masses on plants or in the soil.
The best way to conserve assassin bugs and other natural enemies is to reduce the use of broad-spectrum insecticides in the vineyard. These products kill beneficial insects as well as pests. If insecticides must be used, use narrow-spectrum products that target only the key pest and have minimal impacts on beneficial insects. Integrated pest management (IPM) strategies often include alternative control methods, which minimize or eliminate the use of insecticides altogether.
Recommended Resources
Assassin Bugs, University of California
Beneficial Insects in Vineyards
Reviewed by Erwin A. Elsner, Michigan State University, and Kristine Godfrey, University of California