ACTIVITY AND PERSISTENCE OF STEINERNEMA-CARPOCAPSAE AND SPODOPTERA-EXIGUA NUCLEAR POLYHEDROSIS-VIRUS AGAINST S-EXIGUA LARVAE ON SOYBEAN

Experiments were conducted to assess the effects of the entomopathogen ic nematode Steinernema carpocapsae and Spodoptera exigua multinucleoc apsid nuclear polyhedrosis virus (SeMNPV), alone and in combinations, on mortality of the beet armyworm, S. exigua, larvae on soybean. In 19 91 tests, field-grown soybean plants were treated with S. carpocapsae at 0.3 and 0.6 nematodes/cm(2) of leaflet, SeMNPV at 20 and 40 polyhed ral inclusion bodies (PIB)/cm(2), and all possible combinations. Treat ed leaflets were collected from plants and bioassayed with 5-day-old l arvae. The combination of S. carpocapsae at 0.6 nematodes/cm(2) + SeMN PV at 40 PIB/cm(2) produced significantly higher larval mortality (61. 7%) compared with either S. carpocapsae (24.8-35.1%) or SeMNPV (26.5-3 3.7%) alone. In 1992, similar tests were repeated using S. carpocapsae at 0.2 and 0.5 nematodes/cm(2), and SeMNPV at 14 and 35 PIB/cm(2). Th e combination of 0.5 nematodes/cm(2) + 35 PIB/cm(2) resulted in signif icantly higher larval mortality (64.0%) than either pathogen alone (41 .5-49.0%). Steinernema carpocapsae and SeMNPV produced additive effect s on beet armyworm mortality. Persistence of S. carpocapsae was 12-24 hours and SeMNPV was 96-120 hours on soybean.