INTERACTIVE EFFECTS OF STEINERNEMA-CARPOCAPSAE AND SPODOPTERA-EXIGUA NUCLEAR POLYHEDROSIS-VIRUS ON SPODOPTERA-EXIGUA LARVAE

Laboratory experiments were conducted to assess the interactive effect of the entomopathogenic nematode Steinernema carpocapsae and Spodoptera exigua multinucleocapsid nuclear polyhedrosis virus (SeMNPV) when applied in combination against the beet armyworm, Spodoptera exigua, larvae on soybean. The LC(25) and LC(50) for S. carpocapsae and SeMNPV were determined and tested as single and combination treatments. The LC(25) and LC(50) for S. carpocapsae were 117 and 263 nematodes/ml, respectively, and for SeMNPV were 7.6 x 10(3) and 1.9 x 10(4) polyhedral inclusion bodies/ml, respectively. S. carpocapsae and SeMNPV produced additive effects on beet armyworm mortality in all combination treatments. Combinations of S. carpocapsae + SeMNPV at LC(25) + LC(25) and LC(50) + LC(50) resulted in a significantly higher larval mortality than treatments with either pathogen alone at the corresponding concentrations. Combinations of the pathogens at LC(25) + LC(50) and LC(50) + LC(25) produced a significantly higher larval mortality than treatments with LC(25) of either pathogen alone. However, these mortalities were not significantly different from those in LC(50) treatments of either pathogen alone. The reproductive ability of S. carpocapsae in the infected hosts was not affected by SeMNPV in the combination treatments. These results suggest that treatments with S. carpocapsae + SeMNPV at appropriate combinations of concentration levels may result in greater control of beet armyworm than applications of either pathogen alone, particularly in a soybean ecosystem. (C) 1995 Academic Press, Inc.