LABORATORY TOXICITY AND FIELD EFFICACY OF AC-303,630 (PIRATE(R)) AGAINST BEET ARMYWORM, SPODOPTERA-EXIGUA (HUBNER), LARVAE

The susceptibility of beet armyworm, Spodoptera exigua (Hubner), colle cted from several hosts in various states in the southeastern and west ern United States to the experimental insecticide AC 303,630 (Pirate(R ), American Cyanamid, Princeton, NJ) was examined using soybean (Glyci ne max (L.) Merrill) leaf dip bioassays. Responses of field strains we re compared to those of a laboratory reference strain of beet armyworm maintained by the USDA-ARS-SIML insectary (Stoneville, MS). In the bi oassays using larvae weighing 30-45 mg, 72 h LC50's for AC 303,630 ran ged from 13-31 ppm for the various strains examined. In most instances , concentrations of 50-60 ppm AC 303,630 caused 100% mortality. The la rgest LC50 value (31 ppm) occurred for a South Carolina beet armyworm strain, which was the only strain significantly more tolerant than the reference laboratory colony. Two field experiments also were conducte d to evaluate efficacy of AC 303,630, compared to other experimental a nd recommended insecticides, against beet armyworm on soybean in Louis iana. In both field experiments, beet armyworm control with AC 303,630 (0.168 kg [AI]/ha) was similar to that of thiodicarb (0.54 kg [AI]/ha ), acephate (0.84 or 1.12 kg [AI]/ha), and MK-244 (0.0084 kg [AI]/ha) and significantly greater than permethrin (0.112 kg [AI]/ha), methomyl (0.504 kg [AI]/ha), and deltamethrin (0.0149 kg [AI]/ha) at 6 to 7 d after treatment.