Lots of Japanese beetle look-alikes out there

Based on a soil temperature prediction model, Japanese beetles should be emerging all over Iowa now. We've seen them at nearly all of our ISU Research Farms. Ok, it helps when we use pheromone traps because they are especially attractive. But we like to be able to catch the first adults of the season!

At the same time these beautiful beetles are moving around, many other close relatives are coming out, too. Japanese beetles and other "scarabs" belong in the beetle family called Scarabaeidae. There are about 30,000 scarabs around the world. Even though they are highly diverse and abundant, they have a couple things in common: stout bodies, clubbed antennae, and many have broad front legs for digging. Some scarabs can be metallic or brightly colored, while others blend into the landscape. Adults can be active during the day or night depending on the species. Because of their relative size and body weight, they are clumsy fliers that move short distances. Some scarabs are scavengers that feed on dung, carrion or decomposing organic materials; others are significant plant pests. The larvae are distinctive because they are ALWAYS in a c-shape and commonly called grubs.

Grubs are immature scarab beetles. Note they have three pairs of true legs but lack the fleshy abdominal legs commonly seen on caterpillars. Grubs can be white or transparent, and will always be in a c-shape. Photo by David Cappaert, www.ipmimages.org. 

With several scarabs emerging at the same time, proper identification can be difficult. Here is a quick review of the most common scarabs out in Iowa right now:

Japanese beetle: Adults are just over 1/2 inch in length. These scarabs have one generation per year. They are visually distinct because of the metallic green head and bronze forewings that do not fully cover the abdomen. They also have white tufts of hair along the sides of the abdomen. Adults have a wide host range (>300 plants), including roses, fruit and shade trees, grapes, corn and soybean. Japanese beetles skeletonize leaves by feeding between the veins.

Japanese beetles are metallic, with clubbed antennae and white tufts of hair. Photo by Dorothy E. Pugh. 

Japanese beetles aggregate to feed and mate, leaving skeletonized leaves. Photo by Mark Licht.  

False Japanese beetle. Sometimes called a sandhill chafer, this species is commonly mistaken for Japanese beetle. They are similar in body shape and size (1/2 inch in length), but is not metallic green and bronze. They can have white hair along the sides of the abdomen, but it is more evenly dispersed instead of in tufts. False Japanese beetles have one generation per year. Adults feed on flowers, fruits and leaves of many plants, but are not considered a field crop pest.

False Japanese beetles are hairy scarabs, but not metallic. Photo by Marlin E. Rice.

Masked chafers. There are several species of masked chafers in Iowa. These scarabs have one generation per year. Adults are 1/2 inch in length and oval in shape. Body color can range from dark yellow to tan with dark markings on the head. They can have hairy bodies, wings and legs. Masked chafers are not known to be field crop pests in Iowa. 

Northern masked chafers are hairy and tan scarabs. Photo by Mike Reding and Betsy Anderson, www.ipmimages.org. 

May/June beetles. There are several scarabs with the common names of May or June beetles. Most have a life cycle that takes 2-4 years. Adults are usually larger (1 inch in length) and oval in shape. Body color ranges from red to brown. Adults feed on a wide variety of plant foliage, but they are not considered field crop pests in Iowa. 

June beetles are attracted to street lights at night. Photo by Steven Katovich, www.ipmimages.org.

Just a few other scarabs that you could find out this summer. None would be considered field crop pests. 

Ten-lined June beetle. Photo by Eugene E. Nelson, www.ipmimages.org.

Little bear. Photo by Whitney Cranshaw. 

Bumble flower beetle. Photo by David Cappaert, www.ipmimages.org.