Arthropod abundance in tall fescue, Lolium arundinaceum, pastures containing novel ‘safe’ endophytes

Authors: KEATHLEY, C - University Of Kentucky; POTTER, D - University Of Kentucky

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2011
Publication Date: 12/1/2011
Citation: Keathley, C.P., Potter, D.A. 2011. Arthropod abundance in tall fescue, Lolium arundinaceum, pastures containing novel ‘safe’ endophytes. Journal of Applied Entomology. 136(8):576-587.

Interpretive Summary: Poor livestock performance on tall fescue is linked to infection by a fungal endophyte that enhances grass resistance to stress, including erbivory, while producing ergot alkaloids toxic to vertebrate grazers. Novel ‘safe’ endophyte/grass associations produce no ergot alkaloids yet etain stand persistence, but they could be more susceptible to insect outbreaks. We tested the hypothesis that grass-feeding insects are more abundant in novel endophyte pastures compared with those containing common endophyte. Above- and below-ground herbivores were sampled across two growing seasons in pastures containing common strain endophyte (KY31), novel endophytes (MaxQ or AR584) or endophyte free. We also sampled natural enemies as an indicator of possible tritrophic effects. With a few exceptions, numbers of predatory, chewing (grasshoppers, crickets, caterpillars) or sucking insects (leafhoppers, planthoppers) were similar in common and novel endophyte pastures. Contrary to our hypothesis, Aphrodes spp. leafhoppers were more abundant in KY31 than other pasture types in 2008; their nymphs also were more abundant in KY31 than in MaxQ in 2009. Adults (but not total numbers or nymphs) of another leafhopper, Psammotettix striatus, were less abundant in KY31 than other pasture types in 2009. Popillia japonica and Cyclocephala spp. grubs did not differ in density, weight or instar among the endophyte-containing associations. In feeding assays, armyworm (Mythimna unipuncta) survival was higher on MaxQ and NE9301, and weight gain was higher on NE9301, suggesting armyworm outbreaks could be more severe on such grasses, but that result may not be attributable solely to alkaloids because common strain and endophytefree grasses did not differ in either parameter. Caterpillar abundance did not differ among pasture types in the field. Our results suggest that re-seeding common strain endophytic pastures with livestock-safe novel endophyte/grass associations to alleviate fescue toxicosis is unlikely to promote markedly higher populations of plant-feeding insects.

Technical Abstract: Poor livestock performance on tall fescue is linked to infection by a fungal endophyte that enhances grass resistance to stress, including erbivory, while producing ergot alkaloids toxic to vertebrate grazers. Novel ‘safe’ endophyte/grass associations produce no ergot alkaloids yet etain stand persistence, but they could be more susceptible to insect outbreaks. We tested the hypothesis that grass-feeding insects are more abundant in novel endophyte pastures compared with those containing common endophyte. Above- and below-ground herbivores were sampled across two growing seasons in pastures containing common strain endophyte (KY31), novel endophytes (MaxQ or AR584) or endophyte free. We also sampled natural enemies as an indicator of possible tritrophic effects. With a few exceptions, numbers of predatory, chewing (grasshoppers, crickets, caterpillars) or sucking insects (leafhoppers, planthoppers) were similar in common and novel endophyte pastures. Contrary to our hypothesis, Aphrodes spp. leafhoppers were more abundant in KY31 than other pasture types in 2008; their nymphs also were more abundant in KY31 than in MaxQ in 2009. Adults (but not total numbers or nymphs) of another leafhopper, Psammotettix striatus, were less abundant in KY31 than other pasture types in 2009. Popillia japonica and Cyclocephala spp. grubs did not differ in density, weight or instar among the endophyte-containing associations. In feeding assays, armyworm (Mythimna unipuncta) survival was higher on MaxQ and NE9301, and weight gain was higher on NE9301, suggesting armyworm outbreaks could be more severe on such grasses, but that result may not be attributable solely to alkaloids because common strain and endophytefree grasses did not differ in either parameter. Caterpillar abundance did not differ among pasture types in the field. Our results suggest that re-seeding common strain endophytic pastures with livestock-safe novel endophyte/grass associations to alleviate fescue toxicosis is unlikely to promote markedly higher populations of plant-feeding insects.