Does Modification of Tall Fescue Leaf Texture and Forage Nutritive Value for Improved Livestock Performance Increase Suitability for a Grass‐feeding Caterpillar?

Abstract

Grass breeders are developing new forage‐type 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 fiber 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 first 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, fiber, ash, or N) of pasture grasses will affect their resistance. We also studied feeding site initiation and development of first 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 efficient 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 fiber is unlikely to worsen its damage to pastures.

Host Plant Resistance of Cool-Season (C3) Turfgrasses to Above- and Belowground Feeding by <I>Tipula paludosa</I> (Diptera: Tipulidae)

“…We found Þne textured creeping bentgrass and Þne fescues were negatively correlated with aboveground biomass while coarse textured tall fescues were positively correlated. While we did not directly quantify texture of toughness in these trials, these qualitative differences match well with other studies in which aboveground biomechanical factors affected insect feeding success (Hanley et al 2007, Clissold et al 2009, Keathley and Potter 2011, Hong et al 2012. This study suggests the need for increased attention toward quantiÞcation of the aboveground factors impacting T. paludosa feeding.…”

Behavioral plasticity of a grass-feeding caterpillar in response to spiny- or smooth-edged leaf blades

“…Early instars feed on tall fescue by scraping away tissue on the adaxial leaf surface (window-feeding), but older instars feed on leaf edges. In an earlier study, armyworms grew and developed equally well on a wide range of different fescue cultivars and accessions having smooth or spiny leaf edges (Keathley and Potter 2011). The present study sought an explanation for that unexpected result.…”

“…4). Second instars never fed on the spiny edges, but 10% had fed on intermediate edges and 40% had fed on smooth edges by 48 h. Incidence of window-feeding at 1 h was about 25% lower on spiny blades, which also are relatively thick and tough (Keathley and Potter 2011), than on the other grasses (Fisher's exact test, P = 0.02). Second instars completely removed the adaxial epidermis and mesophyll tissues at their window-feeding sites leaving only a thin layer of abaxial epidermal cells (Fig.…”

“…Test-tube leaf blade (TLB) assay arenas ( Fig. 2b) were constructed to observe window-and edgefeeding (Keathley and Potter 2011). Leaf blades were set up in water picks and taped at the leaf apex as described above.…”

“…Livestock producers are concerned with the structural traits of grasses because livestock consume less and are inefficient digesters of forages with tough, fibrous leaves (Buxton and Mertens 1995). Therefore, grass breeders are developing new forage-type tall fescue cultivars with smoother leaf margins for increased palatability to livestock (Easton et al 1994;Zenk 2002;Keathley and Potter 2011).…”