Bean Leaf Beetle, Ceratoma trifurcata: An adult bean leaf beetle with its typical coloration and markings. (Photo Marlin E. Rice)
The bean leaf beetle (Cerotoma trifurcata) is a member of the leaf beetle family Chrysomelidae and order Coleoptera. It has been known to science for more than 235 years since its description as a new species in 1771 (see Eddy and Nettles 1930). This beetle is typically dark yellow; however, it is often some hue between yellow, orange and red (Herzog 1968, 1973, and Smelser and Pedigo 1991) with black markings.
Adults are small insects about 5 mm (1/5 inch) in length. They often have four, large, quadrangular, black markings on the elytra (wing covers) and a black head (although the frons, or face, is often brown in males). Occasionally these four rectangular marks are reduced to two, or they may be completely absent. The most constant identifying character for this beetle is the presence of a black scutellum (the black triangle behind the pronotum or "neck" region). In addition to female beetles often having a black frons (the male frons is brown), sex can also be determined by examining a male's forelegs (Hammack and French 2007). That is, the base of a male beetle's first tarsal segment has a patch of dense setae (or hairs) that are thought to help the male cling to the back of a female beetle during mating. Female beetles lack this character.
The egg is orange and spindle-shaped. It is not much more than a few millimeters long and a couple millimeters wide.
Bean leaf beetle larvae: Bean leaf beetle larvae (Probably 1st instar) will feed on soybean tissue other than roots in the laboratory. Here they are feeding on soybean cotyledon tissue. The white globules are the fat bodies within the insects body cavity. The dark brown area along the midline of the body is actually food passing through the gut. (Photo Jeff Bradshaw)
The larva is a white and cylindrical insect with a dark brown head and brown sclerite (plate) on the top side of the last abdominal segment (see photo of larva).
As the larva matures it passes through successive stages and the larvae develop more sclerites on more segments. This gives it a somewhat speckled appearance under high magnification.
The pupa is white, immoble and slightly resembles the shape of the adult beetle.