Effects of Crop Residue on the Persistence of Steinernema carpocapsae.

We determined the effects of crop residue on the persistence of an entomopathogenic nematode, Steinernema carpocapsae. During 2 consecutive years, nematodes were applied at rates of 2.5 x 10 and 1.0 x 10 infective juveniles/m(2) to small field plots planted with corn. Nematode persistence was monitored by exposing Galleria mellonella larvae to soil samples from plots with and without crop residue (approximately 75% coverage of soybean stubble). Persistence of S. carpocapsae was significantly greater in crop residue plots than in plots without residue. In crop residue plots that received the higher rate of nematode application, larval mortality did not significantly decrease during the study period (3 to 5 days) and remained above 85%. In nematode-treated plots without crop residue, however, larval mortality fell from over 96% to below 11% and 35% in the first and second trials, respectively. The increased crop residue may have benefited nematode persistence through protection from desiccation or ultraviolet light. We conclude that increased ground cover in cropping systems (e.g., due to reduced tillage) may lead to increased insect pest suppression with entomopathogenic nematodes.