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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 SeM-NPV were 7.6 × 10 3 and 1.9 × 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. carpocapsoe + 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 25 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. |
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