Field tests with controlled infestations of eggs ofDiabrotica virgifera virgiferaLeConte showed that larvae at higher infestation rates were stressed for food. The percentage of insects reaching the adult stage was significantly reduced at infestation rates above 600 eggs per 30.5 cm of row. Adults were significantly smaller at infestation rates above 300 eggs, they were shorter-lived at rates above 600 eggs, and they were less fecund at infestation rates above 1,200 eggs per 30.5 cm of row. These results indicate that high densities of immatures have a deleterious effect on number, size, longevity, and fecundity of adult western corn rootworms.