Diabrotica beetles and rootworms (extended information)


Root clipping and tunneling by the worms may result in tilted, curved stems or lodged plants. Lodging may begin around the midwhorl stage and continue to maturity. In seedlings the beetles eat portions of the leaf margins (D. balteata), leave irregular holes in the tender leaves, and occasionally cut the plant at the base. Leaf feeding on older plants seldom has economic significance. At flowering, however, the beetles (which are active fliers) feed on green silks (D. balteata) and pollen, leading at times to poor seed set. D. virgifera and D. longicornis were recently reported to be vectors of maize chlorotic mottle virus (MCMV) and Stewarts’s wilt bacteria.

Description and life cycle

In the soil around infested plants and in their root systems, one can find the white or creamish-colored, thing, soft, small worms. These have three pairs of legs, brown heads, and a dark brown plate at tbe end opposite the head and vary in length at maturity from 3 mm to about 10 mm. After three molts the larvae develop into soft, white pupae inside cells in the soil, from which the beetles emerge. These vary in size (6 to 9 mm) and color pattern according to species. They lay most of their eggs at soil depths of up to 10 cm. The number of generations in a year (ranging from one to three or four) varies with the species and latitude.