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 Spodopte ra exigua multinucleocapsid nuclear polyhedrosis virus (SeMNPV) when a pplied in combination against the beet armyworm, Spodoptera exigua, la rvae on soybean. The LC(25) and LC(50) for S. carpocapsae and SeMNPV w ere determined and tested as single and combination treatments. The LC (25) and LC(50) for S. carpocapsae were 117 and 263 nematodes/ml, resp ectively, and for SeMNPV were 7.6 x 10(3) and 1.9 x 10(4) polyhedral i nclusion bodies/ml, respectively. S. carpocapsae and SeMNPV produced a dditive effects on beet armyworm mortality in all combination treatmen ts. 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 concentrati ons. Combinations of the pathogens at LC(25) + LC(50) and LC(50) + LC( 25) produced a significantly higher larval mortality than treatments w ith LC(25) of either pathogen alone. However, these mortalities were n ot significantly different from those in LC(50) treatments of either p athogen alone. The reproductive ability of S. carpocapsae in the infec ted hosts was not affected by SeMNPV in the combination treatments. Th ese results suggest that treatments with S. carpocapsae + SeMNPV at ap propriate combinations of concentration levels may result in greater c ontrol of beet armyworm than applications of either pathogen alone, pa rticularly in a soybean ecosystem. (C) 1995 Academic Press, Inc.