EFFECTS OF A NUCLEAR POLYHEDROSIS-VIRUS AND A FLUORESCENT BRIGHTENER ON COLONIES OF SPODOPTERA-EXIGUA (HUBNER)

The beet armyworm, Spodoptera exigua (Hubner), is an important pest wh ich is difficult to control because it is resistant to nearly all regi stered insecticides. A new commercial formulation of a nuclear polyhed rosis virus that is pathogenic to beet armyworm larvae, SPOD-X(R), was tested with and without a fluorescent brightener, Tinopal LPW. The ef fects on larvae from six colonies of the beet armyworm which had recen tly been established from held collections in Georgia, Alabama and Mis sissippi were compared with a laboratory colony which had been maintai ned in the laboratory for 2 years. The LC(50) Was lower in all bioassa ys with SPOD-X in 0.25% Tinopal LPW than with SPOD-X in water, althoug h in 3 of 12 bioassays the difference was not significant based on ove rlapping 95% confidence intervals. The mean LC(50) for SPOD-X in water was 376 polyhedral occlusion bodies per cup (surface area 800 mm(2)). The mean LC(50) for SPOD-X in 0.25% Tinopal LPW was 30 polyhedral occ lusion bodies per cup. The LC(50) for SPOD-X in water was not signific antly different between the laboratory colony and 5 of 6 field-collect ed colonies when bioassayed concurrently. There was no significant dif ference in LC(50) for SPOD-X in 0.25% Tinopal LPW between the laborato ry colony and any of the field-collected colonies. Thus, Tinopal LPW e nhanced the infectivity of SPOD-X for beet armyworm larvae in laborato ry tests and reduced the variability of response of the beet armyworm colonies to the virus.