Biological control of the western corn rootworm (Coleoptera : Chrysomelidae) using the entomopathogenic nematode, Steinernema carpocapsae

A series of field trials evaluated the efficacy of the entomopathogenic nem atode, Steinernema carpocapsae Weiser All strain for control of western cor n rootworm, Diabrotica virgifera virgifera LeConte, larvae. Separate trials examined the effects of nematode application rate and timing on corn rootw orm control in 1991. In the rate trial, S. carpocapsae (0, 10(4), 10(5), 10 (6), and 10(7) nematodes per 30.5 row-cm) was applied as the insect populat ion entered the second instar. Nematode treatment significantly reduced cor n root injury and adult emergence. High application rates (10(6) and 10(7) nematodes per 30.5 row-cm) significantly outperformed low rates (10(4) and 10(5) nematodes per 30.5 row-cm). Nematode treatment (500,000 S. carpocapsa e per 30.5 row-cm) reduced root injury and adult emergence slightly in the timing trial: later applications (second, third instar) were numerically, b ut not significantly, more effective than early (egg, first instar) ones. I n 1992, a factorial trial combined four application dates (egg; first, seco nd, third instar) and five rates (0, 104, 10(5), 10(6), 10(7) S. carpocapsa e per 30.5 row-cm). Later applications (second, and particularly, third ins tar) were significantly more effective than early (egg, first instar) ones. Root injury and adult emergence in control and low rate (10(4) and 10(5) n ematodes per 30.5 row-cm) plots significantly exceeded that in high rate (1 0(6) and 10(7) nematodes per 30.5 row-cm) plots. Commercially acceptable ro ot protection (root injury ratings below 3.0) was provided by 10(6) nematod es per 30.5 cm of row applied to third instars, and by 10(7) nematodes per 30.5 cm of row applied to second and third instars.