Does modifi cation of tall fescue leaf texture and forage nutritive value for improved livestock performance increase suitability for a grass-feeding caterpillar?

Grass breeders are developing new foragetype tall fescue [Schedonorus arundinaceus (Schreb.) Dumort = Lolium arundinaceum (Schreb.) Darbysh., formerly known as Festuca arundinacea Schreb.] cultivars with smoother texture, improved nutritive value, and reduced fi ber for improved livestock performance. We tested if such grasses are also more susceptible to a grass-feeding caterpillar. True armyworms, Pseudaletia unipuncta (Haworth), were reared from fi rst instar to adult on grass clippings from thirteen fescue cultivars or accessions differing in texture (smooth vs. standard), ecotype (northern European vs. Mediterranean), use (pasture vs. turf-type), or provenance to clarify how modifying the texture (edge spines, trichomes, or cellulose margin), thickness, tissue strength, and nutritive value (dry matter, fi ber, ash, or N) of pasture grasses will affect their resistance. We also studied feeding site initiation and development of fi rst instars on intact leaf blades when prevented from exploiting a cut leaf edge. Larvae performed equally well across all groups when reared with grass clippings, despite variation in leaf texture and nutritive value. On intact blades, however, leaf thickness and tissue strength were correlated with reduced feeding site initiation and larval development. Gregarious and window feeding may allow more effi - cient exploitation of common feeding sites on tougher leaves. True armyworm is adapted to feed on a range of structurally-diverse grasses, so increased use of forage-type tall fescue cultivars with smoother texture or reduced fi ber is unlikely to worsen its damage to pastures.