Growth stimulant and antifeedant activity in Bermuda grass affecting the fall armyworm (Lepidoptera: Noctuidae).

Dietary nutrients were identified by mass spectroscopy from chromatographic isolates of the neutral lipid fraction of Bermuda grass, Cynodon dactylon L. (Pers.). These included methyl and ethyl linolenate, vitamin E (γ-tocopherol, α-tocopherol), and the 3 sterols: campestrol, stigmasterol, and sitosterol. Gas liquid capillary chromatographic analyses of these molecules indicated significant differences among the Bermuda grass genotypes, especially in sterol composition. Campestrol was present in most of the genotypes examined with stigmasterol and sitosterol, showing the greatest variability in abundance and occurrence among the Bermuda grass lines. Larvae of fall armyworm, Spodopterafrugiperda (J. E. Smith), fed on diet supplemented with the lipid fraction showed significantly higher larval weight accumulation (28-54%) compared with controls. Larval growth was variably dependent on the genotype or somaclone lipid profile. These findings confirm a major role for neutral lipids in insect growth physiology and, by implication, are key elements in Bermuda grass nutritive value. Additionally, an antifeedant also was isolated from Bermuda grass. A crude sohxlet extract from Bermuda grass (line OSU 71 X6-7) was sequentially fractionated by silica gel flash column and reverse-phase high-pressure'liquid chromatography (HPLC). A bioassay-guided scheme with the fall armyworm yielded an active antifeedant fraction eluting at 10% EtOAc/ CH 2 Cl 2 , from which a single active component was isolated by HPLC. The biological effects of these isolates on neonate fall armyworm larvae included a retardation of larval growth (80% reduction in larval weight) and an increase in duration to pupal metamorphosis (70%) that were significantly different from either control treatments or other chromatographic fractions. A concentration-dependent antifeedant response with the isolate to topically treated diet plugs was observed.